Articles de revues : « Twisted Metal 2 »

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Kozlova, Svetlana, Maxim Ryzhikov, Denis Pishchur et Irina Mirzaeva. « Overview of Low-Temperature Heat Capacity Data for Zn2(C8H4O4)2.C6H12N2 and the Salam Hypothesis ». Symmetry 11, n^o 5 (11 mai 2019) : 657. http://dx.doi.org/10.3390/sym11050657.

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The review presents the progress in the analysis of low-temperature heat capacity of the metal-organic framework Zn2(C8H4O4)2.C6H12N2 (Zn-DMOF). In Zn-DMOF, left-twisted D3(S) and right-twisted D3(R) DABCO molecules (C6H12N2) can transform into each other by tunneling to form a racemate. Termination of tunneling leads to a phase transition in the subsystem of twisted molecules. It is suggested that Zn-DMOF may be considered a model system to study the mechanisms of phase transitions belonging to the same type as hypothetical Salam phase transitions.

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Lu, Ning, Hongyan Guo, Zhiwen Zhuo, Lu Wang, Xiaojun Wu et Xiao Cheng Zeng. « Twisted MX2/MoS2heterobilayers : effect of van der Waals interaction on the electronic structure ». Nanoscale 9, n^o 48 (2017) : 19131–38. http://dx.doi.org/10.1039/c7nr07746g.

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A comprehensive first-principles study of the electronic properties of twisted 2D transition metal dichalcogenide (TMDC) heterobilayers MX₂/MoS₂(M = Mo, Cr, W; X = S, Se) with different rotation angles has been performed.

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Morgunov, Konstantin P., Yuri K. Ivanovsky et Andrey Yu Baranov. « EXPERIMENTAL DETERMINATION OF THE ROUGHNESS COEFFICIENT OF METAL SPIRALLY-TWISTED CORRUGATED PIPES ». Vestnik Gosudarstvennogo universiteta morskogo i rechnogo flota imeni admirala S. O. Makarova 12, n^o 2 (28 avril 2020) : 323–35. http://dx.doi.org/10.21821/2309-5180-2020-12-2-323-335.

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Zhao, Chongchao, Elliot N. Glass, Jordan M. Sumliner, John Bacsa, Daniel Taehyun Kim, Weiwei Guo et Craig L. Hill. « Complexation of metal carbonyl units with [α-PW11O39]7− and [α2-P2W17O61]10− : insights into the chiral “twisted-sandwich” dimeric structures ». Dalton Trans. 43, n^o 10 (2014) : 4040–47. http://dx.doi.org/10.1039/c3dt53374c.

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Capturing [M(CO)₃]⁺ (M = Re, Mn) by [α-PW₁₁O₃₉]⁷⁻ or [α₂-P₂W₁₇O₆₁]¹⁰⁻ leads to polyoxometalate-supported metal carbonyl complexes with chiral “twisted-sandwich” structures.

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Lah, Nina, et Katja Lapanje. « Bromidobis[2-(pyridin-2-yl)methanol-κ2N,O]copper(II) bromide monohydrate ». Acta Crystallographica Section C Crystal Structure Communications 69, n^o 6 (24 mai 2013) : 624–26. http://dx.doi.org/10.1107/s0108270113013437.

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The title compound, [CuBr(C6H7NO)2]Br·H2O, is an ionic mononuclear complex in which the [CuBr(C6H7NO)2]+cation possesses distorted square-pyramidal geometry. The CuIIcentre is coordinated by two neutral 2-(pyridin-2-yl)methanol (2-pyMeOH) ligands and a terminal bromide ligand. The 2-pyMeOH ligands are coordinated in a bidentate chelating manner through the pyridine N and hydroxy O atoms, forming a five-membered chelate ring with the CuIIcentre. The planes of the pyridine rings are twisted by 58.71 (14)° with respect to each other. The charge is balanced by a noncoordinating bromide anion which, together with a solvent water molecule, links the components through hydrogen bonds into infinite chains propagating along theaaxis. The mononuclear cations appear to associate in pairs through weak interactions between the metal atom of one cation and the halogen atom of an adjacent cation.

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Bock, Hans, Sabine Nick, Christian Näther et Wolfgang Bensch. « Wechselwirkungen in Kristallen, 63 [1, 2] Kristallisation und Strukturbestimmung von 1,2-Dimesitoylbenzol und von Bis(hydrogen-1,2-dimesitoylbenzol)-dinatrium-bis(ethylendiamin)/Interactions in Crystals, 63 [1, 2] Crystallization and Structure Determination of 1,2-Dimesitoylbenzene and of Bis(hydrogen-1,2-dimesitoylbenzene)-disodium-bis(ethylendiamine) ». Zeitschrift für Naturforschung B 50, n^o 4 (1 avril 1995) : 605–12. http://dx.doi.org/10.1515/znb-1995-0423.

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Chelate complexes of 1,2-dimesitoylbenzene radical anion with alkali metal cations exhibit in aprotic solution extremely large ESR /ENDOR metal coupling constants. For rationalization, structures of both the neutral molecule (H3C)3H2C6 - CO - C6H4 - CO - C6H2(CH3)3, in which the two carbonyl groups are twisted out of the benzene ring plane by dihedral angles of ± 3̄7̄°, and a sodium contact ion quadruple have been determined. One of the dimers [dimesitoylbenzeneH⊖ (Na⊕H2N H2C - CH2NH2)]2, although generated by Na metal mirror reduction of 1,2-dimesitoylbenzene in aprotic DME solution with added ethylendiamine for better electron transfer, surprisingly contains two 245 pm short (!) hydrogen bridges ⊖O ··· (H)O and in addition two solvation bridges e ⊖O ··· Na⊕(H2NH2C - CH2NH2) ··· O⊖. Results of MNDO calculations based on the experimental coordinates support the proposed concept.

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Wang, Cheng-Hui, Qing Tang, Jing Zhang, Yu-Qing Yao, Xin Xiao, Ying Huang et Zhu Tao. « Alkaline earth cation-mediated photoluminescent complexes of thioflavin T with twisted cucurbit[14]uril ». New Journal of Chemistry 42, n^o 11 (2018) : 9244–51. http://dx.doi.org/10.1039/c7nj04115b.

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The introduction of alkaline earth metal cations into the tQ[14]–ThT interaction system leds to the precipitation of solid tQ[14]/ThT/AE²⁺ interaction products, which emitted strong blue fluorescence.

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Kasyanova, Irina V., Artur R. Geivandov, Vladimir V. Artemov, Maxim V. Gorkunov et Serguei P. Palto. « Nematic liquid crystal alignment on subwavelength metal gratings ». Beilstein Journal of Nanotechnology 9 (4 janvier 2018) : 42–47. http://dx.doi.org/10.3762/bjnano.9.6.

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We have studied the alignment of a nematic liquid crystal (LC) material on aluminum subwavelength nanogratings as a function of the period, p, and the slit width to period ratio, w/p. A method, based on Fourier analysis of the transmittance spectra of the LC grating system, has been applied. We show that the gratings provide stable planar alignment only for shorter periods and narrower slits (p < 400 nm, w/p < 2/3). As these parameters increase, the homogeneous surface alignment changes to domains with different tilt angles or to spatially modulated alignment. We have also obtained a 90° twisted LC director distribution, implying sufficiently strong azimuthal LC anchoring at the grating surface.

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Buchspies, Jonathan, Md Mahbubur Rahman et Michal Szostak. « Transamidation of Amides and Amidation of Esters by Selective N–C(O)/O–C(O) Cleavage Mediated by Air- and Moisture-Stable Half-Sandwich Nickel(II)–NHC Complexes ». Molecules 26, n^o 1 (2 janvier 2021) : 188. http://dx.doi.org/10.3390/molecules26010188.

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The formation of amide bonds represents one of the most fundamental processes in organic synthesis. Transition-metal-catalyzed activation of acyclic twisted amides has emerged as an increasingly powerful platform in synthesis. Herein, we report the transamidation of N-activated twisted amides by selective N–C(O) cleavage mediated by air- and moisture-stable half-sandwich Ni(II)–NHC (NHC = N-heterocyclic carbenes) complexes. We demonstrate that the readily available cyclopentadienyl complex, [CpNi(IPr)Cl] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), promotes highly selective transamidation of the N–C(O) bond in twisted N-Boc amides with non-nucleophilic anilines. The reaction provides access to secondary anilides via the non-conventional amide bond-forming pathway. Furthermore, the amidation of activated phenolic and unactivated methyl esters mediated by [CpNi(IPr)Cl] is reported. This study sets the stage for the broad utilization of well-defined, air- and moisture-stable Ni(II)–NHC complexes in catalytic amide bond-forming protocols by unconventional C(acyl)–N and C(acyl)–O bond cleavage reactions.

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Mihaliková, Mária, Petra Lacková et Anna Lišková. « Analysis of Pearlitic Cold Drawn Steel Wire ». Materials Science Forum 818 (mai 2015) : 288–91. http://dx.doi.org/10.4028/www.scientific.net/msf.818.288.

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The effect of microstructure on the mechanical properties of cord steel wires was investigated. Material properties and damage behaviours were identified. Metal cord, for reinforcing articles of an elastomeric material, such as tires, conveyor belts and so on of the single strand type, in particular made up of a plurality of 3, 4 or 6 wires, where in the said wires are twisted together loosely. The metal cord characterized by the fact that the diameter of the individual constituent wires varies between 0.12 and 0.30 mm. Rm tested cord wire was max. 2 946 MPa. Fracture surfaces cords steels were observed.

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Lemke, Matthias, Falk Knoch et Horst Kisch. « Charge - Transfer Complexes of Metal Dithiolenes XXIV : Ion Pairs of the Tetrakis(dimethylamino)ethene Dication with Dithiolene Metalate Dianions ». Zeitschrift für Naturforschung B 52, n^o 1 (1 janvier 1997) : 65–68. http://dx.doi.org/10.1515/znb-1997-0113.

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The dication of tetrakis(dimethylamino)ethene (TDAE2+) forms ion pair complexes with [M(mnt)2]2-, mnt2-= maleonitrile-2,3-dithiolate, M(II) = Ni, Pd, Pt, and Zn. According to X-ray analysis the structure of {TDAE2+[Pt(mnt)2]2- } consists of a chain-like arrangement of planar dianions and twisted (71°) dications. Shortest interionic contacts are 11 pm longer than the corresponding van der Waals radii. In the UV-VIS diffuse reflectance spectra of the complexes with a d8 central metal there is no unambiguous evidence for the presence of an ion pair CT band. This band is observed, however, at 450 nm when the d10 metal Zn(II) is present. Application of the Hush-Marcus model affords a reorganization energy of 110 kJ / mol for electron transfer from [Zn(mnt)2]2- to TDAE2+. This value is 40 kJ / mol higher than the one reported for the analogous complex wherein TDAE2+ is replaced by a 2,2′-bipyridinium acceptor of similar reduction potential

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BAKHSHIEV, I. I., et E. V. KAMALEEV. « FINDINGS ON THE COMPOSITION OF NON-FERROUS METAL OBTAINED FROM THE BURIAL GROUNDS OF THE BRONZE AGE IN THE SOUTH URALS (TAVLYKAEVO 1-2, STARO-YABALAKLY) ». Izvestia Ufimskogo Nauchnogo Tsentra RAN, n^o 4 (11 décembre 2020) : 79–85. http://dx.doi.org/10.31040/2222-8349-2020-0-4-79-85.

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The article presents the results of elemental analysis of the composition of metal objects obtained from the burial grounds dating back to the Srubna culture of the South Urals. The data were received through analyzing the most common category of jewelry - bronze bracelets. The prevailing shapes are open grooved bracelets with rounded ends, as well as bracelets made of rods and twisted wires with semicircular and triangular sections. The main purpose of this work is to give a general description of the oldest metal composition and compare the series of findings from the Cis-Urals and Trans-Urals. The first stage of the work involved examination of 10 samples of the Trans-Ural group of objects from Tavlykaevo 1 and 2 burials and 7 decorations from the Srubna burials of the Staro-Yabalakly necropolis (Cis-Urals). The principal metallurgical group includes tin bronzes with three-component alloys of copper, tin and lead or copper, tin and antimony. In terms of its composition, the series of findings under study was quite clearly differentiated. In the Trans-Ural assemblages, objects with addition of lead were primarily found in the burials of Tavlykaevo I burial ground, while in Tavlykaevo 2 burial ground, copper-tin alloys with antimony inclusions prevailed. In the Staro-Yabalakly necropolis, a single object might contain an admixture of antimony and lead. Depending on the elemental composition of non-ferrous metals in various categories of objects, it is hypothetically possible to reconstruct the directions of metal supply to the South Urals and characterize the local features of the metallurgy development in this region in the Bronze Age.

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Fedotov, Alexander K., Sergey L. Prishchepa, Alexander S. Fedotov, Vladzislaw E. Gumennik, Ivan V. Komissarov, Artem O. Konakov, Svetlana A. Vorobyova, Andrei A. Kharchenko et Oleg A. Ivashkevich. « Effect of cobalt particle deposition on quantum corrections to Drude conductivity in twisted CVD graphene ». Modern Electronic Materials 5, n^o 4 (31 décembre 2019) : 165–73. http://dx.doi.org/10.3897/j.moem.5.4.52068.

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Graphene applications in electronics require experimental study of the formation of high-quality Ohmic contacts and deeper understanding of electron transport mechanisms at metal/grapheme contacts. We have studied carrier transport in twisted CVD graphene decorated with electrodeposited Co particles forming Ohmic contacts with graphene layers. We have compared layer resistivity as a function of temperature and magnetic field R�(T, B) for as-synthesized and decorated twisted graphene on silicon oxide substrates. Experiments have proven the existence of negative (induction < 1 Tl) and positive (induction > 1 Tl) contributions to magnetoresistance in both specimen types. The R�(T, B) functions have been analyzed based on the theory of 2D quantum interference corrections to Drude conductivity taking into account competition of hopping conductivity mechanism. We show that for the experimental temperature range (2–300 K) and magnetic field range (up to 8 Tl), carrier transport description in test graphene requires taking into account at least three interference contributions to conductivity, i.e., from weak localization, intervalley scattering and pseudospin chirality, as well as graphene buckling induced by thermal fluctuations.

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Dong, Shin-Shan, et Chen-I. Yang. « A Three-Dimensional Nickel(II) Framework from a Semi-Flexible Bipyrimidyl Ligand Showing Weak Ferromagnetic Behavior ». Polymers 11, n^o 1 (11 janvier 2019) : 119. http://dx.doi.org/10.3390/polym11010119.

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A semi-flexible bipyrimidyl ligand, 5,5′-bipyrimidin (bpym), was used for the self-assembly of a transition metal coordination polymer, resulting in the formation of a nickel(II) compound, [Ni(Br)2(bpym)2]n (1) with a three-dimemsional (3D) structure. Single-crystal X-ray analysis showed that compound 1 crystallizes in the monoclinic space group C2/c and the structure represents a 3D (4,4)-connected bbe topological framework constructed of nickel(II) ions, twisted cis-μ-bpym and planar trans-μ-bpym groups. Magnetic characterization revealed that 1 shows antiferromagnetic coupling between the pyrimidyl-bridged Ni(II) ions along with weak ferromagnetism due to spin canting with a magnetic ordering below Tc = 3.4 K.

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Jang, Chun Keun, et Jae Yun Jaung. « Synthesis and optical properties of tetrapyrazinoporphyrazine containing phenylene dendron unit as a peripheral substituent ». Journal of Porphyrins and Phthalocyanines 13, n^o 08n09 (août 2009) : 939–48. http://dx.doi.org/10.1142/s1088424609001285.

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A dendritic shell can create a distinct micro-environment within its core. It also has the advantage of possessing unique photochemical, photophysical, electrochemical, and catalytic properties. Polyphenylene dendrons, which are characterized by their shape-persistent structures and out-of-plane twisted phenyl components, have previously been successfully attached to various functional groups. We have recently developed a convenient method for synthesizing a new type of porphyrazine that contains both flexible (linear) and more rigid (dendritic) groups. The synthesis of this completely aromatic and dendronic structure is unique in that it is based on a [2+4] Diels-Alder cycloaddition of tetraphenylcyclopentadienone to an ethynyl compound, followed by the elimination of carbon monoxide. In this study, tetrapyrazinoporphyrazinato metal and metal-free complexes were prepared by mixing 2,3-dicyano-5-polyphenylpyrazines with magnesium in n-butanol. The synthesized tetrapyrazinoporphyrazines were characterized by UV-visible spectroscopy, MALDI-TOF-MS (matrix-assisted laser desorption/ionization time-of-flight mass) spectrometry, elemental analysis and 1 H NMR spectroscopy.

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Konoplitskyi, Viktor S., et Yurii Ye Korobko. « ASSESSMENT OF THE INFLUENCE OF UTERINE APPENDAGES TORSION ON THEIR PATHOMORPHOLOGICAL CHANGES IN THE EXPERIMENT ». Wiadomości Lekarskie 74, n^o 8 (2021) : 1876–84. http://dx.doi.org/10.36740/wlek202108117.

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The aim: The study of pathomorphological changes in uterine appendages during torsion of different duration and after their detorsion in the experiment on rats. Materials and methods: Experimental studies were performed on the basis of vivarium in the conditions of chronic experiment on 48 females of outbred white rats weighing 200.0 ± 20.0 grams.The essence of the experimental model is that the female rats, under the ketamine’s anesthesia at the rate of 1-2 mg / kg of the drug, conduct a right-sided ovary twist at 7200 in the projection of the oviduct with fixation of the organs with an external clip of indifferent metal. Results: After ovarian detorsion, until 72 hours after its torsion, reliable reversible restoration of the structural components of the ovary is determined as a positive consequence of the effect of the correction factor (detorsion). Conclusions: The data obtained in the experiment showed that there was a discrepancy between the macroscopic features of the twisted uterine appendages and the microscopic changes in their morphological examination. Despite the presence of external signs of necrosis in the tissue of the uterine appendages, after the detorsion and the restoration of blood flow in them, studies have shown the possibility of performing organ-saving surgical operations in the torsion of the uterine appendages.

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Granifo, Juan, Beatriz Arévalo, Rubén Gaviño, Sebastián Suárez et Ricardo Baggio. « Structural and theoretical characterization of a new twisted 4′-substituted terpyridine compound : 4′-(isoquinolin-4-yl)-2,2′:6′,2′′-terpyridine ». Acta Crystallographica Section C Structural Chemistry 72, n^o 12 (4 novembre 2016) : 932–38. http://dx.doi.org/10.1107/s2053229616016533.

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4′-Substituted derivatives of 2,2′:6′,2′′-terpyridine with N-containing heteroaromatic substituents, such as pyridyl groups, might be able to coordinate metal centres through the extra N-donor atom, in addition to the chelating terpyridine N atoms. The incorporation of these peripheral N-donor sites would also allow for the diversification of the types of noncovalent interactions present, such as hydrogen bonding and π–π stacking. The title compound, C24H16N4, consists of a 2,2′:6′,2′′-terpyridine nucleus (tpy), with a pendant isoquinoline group (isq) bound at the central pyridine (py) ring. The tpy nucleus deviates slightly from planarity, with interplanar angles between the lateral and central py rings in the range 2.24 (7)–7.90 (7)°, while the isq group is rotated significantly [by 46.57 (6)°] out of this planar scheme, associated with a short Htpy...Hisqcontact of 2.32 Å. There are no strong noncovalent interactions in the structure, the main ones being of the π–π and C—H...π types, giving rise to columnar arrays along [001], further linked by C—H...N hydrogen bonds into a three-dimensional supramolecular structure. An Atoms In Molecules (AIM) analysis of the noncovalent interactions provided illuminating results, and while confirming the bonding character for all those interactions unquestionable from a geometrical point of view, it also provided answers for some cases where geometric parameters are not informative, in particular, the short Htpy...Hisqcontact of 2.32 Å to which AIM ascribed an attractive character.

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Laus, Gerhard, Klaus Wurst, Volker Kahlenberg, Holger Kopacka, Christoph Kreutz et Herwig Schottenberger. « N-Heterocyclic Carbene (NHC) Derivatives of 1,3-Di(benzyloxy)imidazolium Salts ». Zeitschrift für Naturforschung B 65, n^o 7 (1 juillet 2010) : 776–82. http://dx.doi.org/10.1515/znb-2010-0702.

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1-Hydroxyimidazole-3-oxide (1) was alkylated with benzyl bromide in the presence of NaHCO3 to give the new 1,3-di(benzyloxy)imidazolium bromide 2a which was converted to the hexafluorophosphate 2b and bis(trifluoromethylsulfonyl)imide 2c. From this cation, pyridine generated a carbene which was trapped by sulfur or selenium to yield the respective 2-thione 3 or 2-selone 4. Bromination afforded the 2-bromo derivative 5. Reaction of the hexafluorophosphate 2b with silver oxide gave the silver-N-heterocyclic carbene complex 6 which was transmetallated with Au(Me2S)Cl to the gold-carbene complex 7. A rhodium-carbene complex 8 was obtained by reaction of the hexafluorophosphate 2b with [Rh(cod)Cl]2 in the presence of triethylamine. Eight crystal structures were determined by X-ray diffraction. The N-benzyloxy groups are twisted out of the plane of the imidazole ring in the solid state. They adopt syn conformations in the cation of the hexafluorophosphate 2b and in the metal-carbene complexes 6 - 8, but anti conformations in the thione 3 and selone 4. Both conformations were observed in two polymorphs of the 2-bromo compound 5.

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Chernyshev, Victor M., Anna V. Chernysheva, Raisa S. Abagyan et Victor B. Rybakov. « Crystal structure of bis[(5-amino-1H-1,2,4-triazol-3-yl-κN4)acetato-κO]diaquanickel(II) dihydrate ». Acta Crystallographica Section E Structure Reports Online 70, n^o 11 (4 octobre 2014) : 286–89. http://dx.doi.org/10.1107/s1600536814021436.

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The title compound, [Ni(C4H5N4O2)2(H2O)2]·2H2O, represents the first transition metal complex of the novel chelating triazole ligand, 2-(5-amino-1H-1,2,4-triazol-3-yl)acetic acid (ATAA), to be structurally characterized. In the molecule of the title complex, the nickel(II) cation is located on an inversion centre and is coordinated by two water molecules in axial positions and two O and two N atoms from twotrans-oriented chelating anions of the deprotonatedATAAligand, forming a slightly distorted octahedron. Thetransangles of the octahedron are all 180° due to the inversion symmetry of the molecule. Thecis-angles are in the range 87.25 (8)–92.75 (8)°. The six-membered chelate ring adopts a slightly twisted boat conformation with puckering parametersQ= 0.542 (2) Å, Θ = 88.5 (2) and ϕ = 15.4 (3)°. The molecular conformation is stabilized by intramolecular N—H...O hydrogen bonds between the amino group and the chelating carboxylate O atom of twotrans-oriented ligands. In the crystal, the complex molecules and lattice water molecules are linked into a three-dimensional framework by an extensive network of N—H...O, O—H...O and O—H...N hydrogen bonds.

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Wang, Xu, Jung Sup Lee et Dong-Sheng Yang. « High-resolution electron spectroscopy and molecular structures of Cu–(2,2′-bipyridine) and Cu-(4,4′-bipyridine) ». Canadian Journal of Chemistry 91, n^o 7 (juillet 2013) : 613–20. http://dx.doi.org/10.1139/cjc-2012-0543.

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Copper complexes of 2,2′-bipyridine (22BIPY) and 4,4′-bipyridine (44BIPY) were prepared in a laser-vaporization supersonic molecular beam source and identified by laser photoionization time-of-flight mass spectrometry. Electronic spectra and molecular structures were studied with pulsed-field ionization zero electron kinetic energy (ZEKE) electron spectroscopy, density functional theory (DFT) and second-order Møller–Plesset perturbation (MP2) calculations, and spectral simulations. Adiabatic ionization energies and metal–ligand and ligand-based vibrational frequencies of Cu–22BIPY and Cu–44BIPY were measured from the ZEKE spectra. Ground electronic states and molecular structures of the two complexes were determined by comparing the spectroscopic measurements with the theoretical calculations. The ground state of Cu–22BIPY ( 2 B1, C2v) has a planar bidentate structure with Cu binding to two nitrogen atoms and two pyridine molecules in the cis configuration. The ground state of Cu–44BIPY ( 2 A, C2) has a monodentate structure with Cu binding to one nitrogen and two pyridines in a twisted configuration. The ionization energy of Cu–22BIPY is considerably lower and its bond energy is much higher than that of Cu–44BIPY. The different ionization and dissociation energies are attributed to the distinct metal binding modes of the two complexes. It has been found that the DFT calculations yield the correct structures for the Cu–22BIPY complex, whereas the MP2 calculations produce the best structures for the Cu–44BIPY complex.

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Wüstefeld, Hans-Ulrich, William C. Kaska, Ferdi Schüth, Galen D. Stucky, Xianhui Bu et Bernt Krebs. « Transition Metal Complexes with the Proton Sponge 4,9-Dichloroquino[7,8-h]quinoline : Highly Twisted Aromatic Systems and an Extreme “Out-of-Plane” Position of the Coordinated Transition Metal Atom ». Angewandte Chemie International Edition 40, n^o 17 (3 septembre 2001) : 3182–84. http://dx.doi.org/10.1002/1521-3773(20010903)40:17<3182 ::aid-anie3182>3.0.co;2-j.

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Low, Pauline M. N., Agnes L. Tan, T. S. Andy Hor, Yuh-Sheng Wen et Ling-Kang Liu. « Substituted Metal Carbonyls. 27.1Synthesis, Structures, and Metal−Metal Bonding of a Ferrocenylphosphineexo-Bridged Cluster with Two Heterometallic Triangles, [AuMn2(CO)8(μ-PPh2)]2(μ-dppf), and a Twisted-Bowtie Cluster, PPN+[Au{Mn2(CO)8(μ-PPh2)}2]-(dppf = 1,1‘-Bis(diphenylphosphino)ferrocene) ». Organometallics 15, n^o 11 (mai 1996) : 2595–603. http://dx.doi.org/10.1021/om950797g.

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Karmakar, Anirban, Anup Paul, Elia Pantanetti Sabatini, M. Fátima C. Guedes da Silva et Armando J. L. Pombeiro. « Pyrene Carboxylate Ligand Based Coordination Polymers for Microwave-Assisted Solvent-Free Cyanosilylation of Aldehydes ». Molecules 26, n^o 4 (19 février 2021) : 1101. http://dx.doi.org/10.3390/molecules26041101.

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The new coordination polymers (CPs) [Zn(μ-1κO1:1κO2-L)(H2O)2]n·n(H2O) (1) and [Cd(μ4-1κO1O2:2κN:3,4κO3-L)(H2O)]n·n(H2O) (2) are reported, being prepared by the solvothermal reactions of 5-{(pyren-4-ylmethyl)amino}isophthalic acid (H2L) with Zn(NO3)2.6H2O or Cd(NO3)2.4H2O, respectively. They were synthesized in a basic ethanolic medium or a DMF:H2O mixture, respectively. These compounds were characterized by single-crystal X-ray diffraction, FTIR spectroscopy, thermogravimetric and elemental analysis. The single-crystal X-ray diffraction analysis revealed that compound 1 is a one dimensional linear coordination polymer, whereas 2 presents a two dimensional network. In both compounds, the coordinating ligand (L2−) is twisted due to the rotation of the pyrene ring around the CH2-NH bond. In compound 1, the Zn(II) metal ion has a tetrahedral geometry, whereas, in 2, the dinuclear [Cd2(COO)2] moiety acts as a secondary building unit and the Cd(II) ion possesses a distorted octahedral geometry. Recently, several CPs have been explored for the cyanosilylation reaction under conventional conditions, but microwave-assisted cyanosilylation of aldehydes catalyzed by CPs has not yet been well studied. Thus, we have tested the solvent-free microwave-assisted cyanosilylation reactions of different aldehydes, with trimethylsilyl cyanide, using our synthesized compounds, which behave as highly active heterogeneous catalysts. The coordination polymer 1 is more effective than 2, conceivably due to the higher Lewis acidity of the Zn(II) than the Cd(II) center and to a higher accessibility of the metal centers in the former framework. We have also checked the heterogeneity and recyclability of these coordination polymers, showing that they remain active at least after four recyclings.

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Curtis, Neil F., Olga P. Gladkikh, David C. Weatherburn, John S. De Courcey et T. Neil M. Waters. « Compounds of Copper(II) and Nickel(II) with 6,8,8,13,13,15-Hexamethyl-1,2,4,5,9,12- hexaazacyclopentadeca-5,15(1)-diene and Some 3-Substituted Homologues ». Australian Journal of Chemistry 51, n^o 7 (1998) : 611. http://dx.doi.org/10.1071/c97024.

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Copper(II) and nickel(II) compounds, [M(L)]2+, of the macrocyclic ligand 6,8,8,13,13,15-hexamethyl-1,2,4,5,9,12-hexaazacyclopentadeca-5,15(1)-diene are formed by reaction of compounds of 4,4,9,9-tetramethyl-5,8-diazadodecane-2,11-dione dihydrazone with methanal. Analogous reactions with aldehydes RHCO, or ketones RR′CO, form compounds of 3-R or 3-RR′ substituted ligands, [M(r- L)]2+ or [M(rr′-L)]2+, respectively. The nickel(II) cations form singlet ground state salts, e.g. [Ni(L)]X2, X = [ClO4]- or ½[ZnCl4]2-, and also triplet ground state compounds, e.g. [Ni(L) (NCS)2] and [Ni(L)(X)] (ClO4) (X = NO2-, C2O42-, N3-, etc.). The structures of [Cu(L)] (ClO4)2, [Ni(L)] (ClO4)2, the 3-propyl compound formed from butanal, [Cu(pr-L)] (ClO4)2.H2O, and the compounds of 9,11,11,16,16,18-hexamethyl-7,8,12,15,19,20-hexaazaspiro[5.14]eicosa-8,18(1)-diene (chex-L), formed from cyclohexanone, namely [Cu(chex-L)] (ClO4)2.MeOH, [Ni(chex-L)] (ClO4)2, and [Ni(chex-L)] (ClO4)2.MeOH, were determined. All have the metal ions in tetrahedrally twisted square-planar coordination, by N1, N5, N9 and N12 , with N9N12-rac, for the (L) and (pr-L) compounds, or by the structurally equivalent N3, N7, N10 and N14, with N7N10-rac, for the (chex-L) compounds. The [Cu(L)]2+ and [Cu(pr-L)]2+cations have saddle-like macrocycle conformations, with approximate mirror symmetry, while the other compounds have ′twisted′ macrocycle conformations with approximate twofold symmetry {[Cu(L)] (ClO4)2, C15H32Cl2CuN6O8, orthorhombic,P 212121, a 8·562(7), b 13·096(8), c 20·257(6) Å, Z 4, R 0·041 for 1540 reflections; [Ni(L)] (ClO4)2, C15H32Cl2N6NiO8, orthorhombic, P21/n, a 13·500(3), b 9·207(2), c 19·478(5) Å, β 103·94(2)°, Z 4, R1 0·055 for 2650 reflections; [Cu(Pr-L)] (ClO4)2.H2O, C18H40Cl2CuN6O9, monoclinic, C 2, a 24·229(5), b 13·780(3), c 8·877(2) Å, β 108·79(3)°, Z 4, R1 0·067 for 1765 reflections; [Cu(chex-L)] (ClO4)2.MeOH, C21H44Cl2CuN6O9, monoclinic, C 2/c, a 17·086(5), b 24·539(2), c 14·496(1) Å, β 89·94(2), Z 8, R1 0·072 for 2521 reflections; [Ni(chex-L)] (ClO4)2, C20H40Cl2N6NiO8, monoclinic, P 21/c, a 14·820(2), b 18·599(4), c 10·282(1) Å, β 106·26(1)°, Z 4, R1 0·067 for 2552 reflections; [Ni(chex-L)] (ClO4)2.MeOH, C21H44Cl2CuN6O9, monoclinic, C 2/c, a 14·451(2), b 24·11(2), c 16·740(3) Å, β 90·14(1)°, Z 8, R1 0·064 for 2598 reflections}.

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Rein, Francisca N., Weizhong Chen, Brian L. Scott et Reginaldo C. Rocha. « Crystal structure and redox potentials of the tppz-bridged {RuCl(bpy)}+ dimer ». Acta Crystallographica Section E Crystallographic Communications 74, n^o 9 (16 août 2018) : 1250–53. http://dx.doi.org/10.1107/s2056989018011258.

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We report the structural and electrochemical characterization of the binuclear complex [μ-(C24H16N6){RuCl(C10H8N2)}2](PF6)2, which contains the bis-tridentate bridging ligand 2,3,5,6-tetrakis(pyridin-2-yl)pyrazine (tppz), the monodentate ligand Cl−, and the bidentate ligand 2,2′-bipyridine (bpy) {systematic name: μ-2,3,5,6-tetrakis(pyridin-2-yl)pyrazine-bis[(2,2′-bipyridine)chloridoruthenium(II)] bis(hexafluoridophosphate)}. The complete [(bpy)(Cl)Ru(tppz)Ru(Cl)(bpy)]2+ dication is generated by crystallographic twofold symmetry; the tppz bridging ligand has a significantly twisted conformation, with an average angle of 42.4° between the mean planes of adjacent pyridyl rings. The metal-coordinated chloride ligands are in a trans configuration relative to each other across the {Ru(tppz)Ru} unit. The RuII ion exhibits a distorted octahedral geometry due to the restricted bite angle [160.6 (3)°] of the tppz ligand. For bpy, the bond lengths of the Ru—N bonds are 2.053 (8) and 2.090 (8) Å, with the shorter bond being opposite to Ru—Cl. For the tridentate tppz, the Ru—N distances involving the outer N atoms trans to each other are 2.069 (8) and 2.072 (9) Å, whereas the Ru—N bond involving the central N atom has the much shorter length of 1.939 (7) Å as a result of the geometric constraints and stronger π-acceptor ability of the pyrazine-centered bridge. The Ru—Cl distance is 2.407 (3) Å and the intramolecular distance between Ru centers is 6.579 (4) Å. In the crystal, weak C—H...Cl and C—H...F interactions consolidate the packing.

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Mendoza, María de los Angeles, Sylvain Bernès et Guillermo Mendoza-Díaz. « Coordination of bis(pyrazol-1-yl)amine to palladium(II) : influence of the co-ligands and counter-ions on the molecular and crystal structures ». Acta Crystallographica Section E Crystallographic Communications 71, n^o 1 (1 janvier 2015) : 22–27. http://dx.doi.org/10.1107/s205698901402595x.

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The structures of a series of complexes with general formulan[Pd(pza)X]Y·mH2O (n= 1, 2;X= Cl, Br, I, N3, NCS;Y= NO3, I, N3, [Pd(SCN)4];m= 0, 0.5, 1) have been determined, where pza is the tridentate ligand bis[2-(3,5-dimethylpyrazol-1-yl)ethyl]amine, C14H23N5. In all complexes, {bis[2-(3,5-dimethylpyrazol-1-yl-κN2)ethyl]amine-κN}chloridopalladium nitrate, [Pd(pza)Cl]NO3, (1), {bis[2-(3,5-dimethylpyrazol-1-yl-κN2)ethyl]amine-κN}bromidopalladium nitrate, [Pd(pza)Br]NO3, (2), {bis[2-(3,5-dimethylpyrazol-1-yl-κN2)ethyl]amine-κN}iodidopalladium iodide hemihydrate, [Pd(pza)I]I·0.5H2O, (3), azido{bis[2-(3,5-dimethylpyrazol-1-yl-κN2)ethyl]amine-κN}palladium azide monohydrate, [Pd(pza)N3]N3·H2O, (4), and bis[{bis[2-(3,5-dimethylpyrazol-1-yl-κN2)ethyl]amine-κN}(thiocyanato-κN)palladium] tetrakis(thiocyanato-κS)palladate, [Pd(pza)NCS]2[Pd(SCN)4], (5), the [Pd(pza)X]+complex cation displays a square-planar coordination geometry, and the pza ligand is twisted, approximating twofold rotation symmetry. Although the pza ligand is found with the same conformation along the series, the dihedral angle between pyrazole rings depends on the co-ligandX. This angle span the range 79.0 (3)–88.6 (1)° for the studied complexes. In (3), two complex cations, two I−anions and one water molecule of crystallization are present in the asymmetric unit. In (5), the central amine group of pza is disordered over two positions [occupancy ratio 0.770 (18):0.230 (18)]. The complex [Pd(SCN)4]2−anion of this compound exhibits inversion symmetry and shows the Pd2+transition metal cation likewise in a square-planar coordination environment. Compound (5) is also a rare occurrence of a non-polymeric compound in which the pseudohalide ligand NCS−behaves both as thiocyanate and isothiocyanate,i.e.is coordinating either through the N atom (in the cation) or the S atom (in the anion).

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Böttcher, Arnd, Horst Elias, Brigitte Eisenmann, Elke Hilms, Andreas Huber, Rüdiger Kniep, Caroline Röhr, Margareta Zehnder, Markus Neuburger et Johan Springborg. « A Novel Synthetic Approach to Asymmetric Salen, Dihydrosalen, and Tetrahydrosalen Ligands : Structures and O2-Activating Properties of their Nickel(II) and Cobalt(II) Complexes ». Zeitschrift für Naturforschung B 49, n^o 8 (1 août 1994) : 1089–100. http://dx.doi.org/10.1515/znb-1994-0814.

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A synthetic procedure is described for the preparation of the tetradentate N2O2 ligands H2[H4]L1=6-(2-hydroxyphenyl)-2,5-diaza-3,3-dimethyl-1-(2-hydroxy-3-t-butyl-5-methyl- phenyl)heptane, H2[H2]L1 = 6-(2-hydroxyphenyl)-2,5-diaza-3,3-dimethyl-1-(2-hydroxy-3-t-butyl-5-methylphenyl)-1-heptene, and H2L1 = 6-(2-hydroxyphenyl)-2,5-diaza-3,3-dimethyl-1-(2- hydroxy-3-t-butyl-5-methylphenyl)-1,5-heptadiene, which are asymmetric derivatives of the ligands tetrahydrosalen, dihydrosalen, and salen. Complexes Ni[H4]L1, Ni[H2]L1, NiL1, CoL1, Ni[H4]L2 (([H4]L2)2- = anion of H2[H4]L2 = N,N'-bis(2-hydroxy-3-t-butyl-5-methylbenzyl)- trans-(S,S)-1,2-diaminocyclohexane), and NiL2 were prepared, characterized (VIS and IR absorption, magnetic moment) and subjected to spectrophotometric titration with pyridine, to determine the equilibrium constants for adduct formation. Single crystal X-ray structure analyses were carried out for Ni[H2]L1 (monoclinic, P21/n; a = 8.926(4), b = 29.324(7), c = 8.411(4) Å; β = 95.3(1)°; Z = 4), CoL1 (monoclinic, C2/c; a = 25.389(2), b = 18.139(2), c = 10.179(1) Å; β = 112.227(6); Z = 8), and Ni[H4]L2·acetone (tetragonal, P41212; a = 13.928(3), c = 33.698(5) Å; Z = 8). In all of the three complexes, the N2O2-metal coordination core is square-planar. The skeleton of the tetradentate ligand is more or less twisted. The planar cobalt(II) complex CoL1 is a low spin d7 system with μexp = 2.02 BM at 298 K, whereas the planar complexes NiL1, Ni[H2]L1 and Ni[H4]L2 are diamagnetic (μexp = 0.28-0.64 BM). The blue solvate Ni[H4]L1- 3EtOH · H2O is paramagnetic (μexp = 3.04 BM), which points to octahedral coordination. In aerated acetone solution, the tetrahydrosalen-type complex Ni[H4]L1 activates dioxygen and one C-N bond is oxidatively dehydrogenated. The VIS spectrum of the dihydrosalen-type complex formed is virtually identical with that of the aldimine complex Ni[H2]L1. In the presence of dioxygen, Co[H4]L1 and Co[H2]L1 are readily oxidized to CoL1 in acetone solution.

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Field, John S., Jan-André Gertenbach, Deogratius Jaganyi, David R. McMillin, Aishath Shaira et David J. Stewart. « Photophysics of [Pt{4-(o-tolyl)isqbipy}Cl]SbF6, where 4-(o-Tolyl)isqbipy is the New 4-(o-Tolyl)-6-(3´´ -isoquinolyl)-2,2´-bipyridyl Ligand ». Zeitschrift für Naturforschung B 65, n^o 11 (1 novembre 2010) : 1318–26. http://dx.doi.org/10.1515/znb-2010-1105.

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The synthesis and characterisation of the 4-(o-tolyl)-6-(3´´-isoquinolyl)-2,2´-bipyridyl [4-(otolyl) isqbipy] ligand is described. A single-crystal X-ray structure determination shows that it adopts a trans-trans conformation about the interannular bonds linking the central pyridine ring to the outer pyridine ring and the isoquinolyl moiety. The o-tolyl group is twisted by an angle of 51.7° out of the plane of the central pyridine ring. The synthesis and characterisation of the [Pt{4-(otolyl) isqbipy}Cl]SbF6 complex is described. The absorption spectrum of the complex measured in acetonitrile exhibits MLCT bands at 362 and 393 nm, as well as intraligand π-π* absorptions in the 200 - 350 nm range; the MLCT bands are shifted significantly to higher energy when compared to those recorded for the parent trpy complex, viz. [Pt{4´-(o-tolyl)trpy}Cl]SbF6, where trpy is 2,2´ : 6´,2´´-terpyridine. Similarly, the 3MLCT emission measured for the 4-(o-tolyl)isqbipy complex in a 1 : 1 CH2Cl2/CHCl3 solution is blue-shifted with respect to the emission spectrum recorded for the 4´-(o-tolyl)trpy complex. We attribute the higher energy MLCT absorption and emission for the 4-(o-tolyl)isqbipy complex to a significantly higher energy for its π*-LUMO than for that of the 4´-(o-tolyl)trpy complex. Emission spectra of the title compound have also been measured in a low-temperature 1 : 5 : 5 (v/v) DMF/methanol/ethanol (DME) glass as a function of concentration. These spectra show that aggregation of the complex occurs at rather low concentrations of 5 - 10 μM, probably to dimers. Variable-temperature emission spectra recorded on a solid sample of [Pt{4-(otolyl) isqbipy}Cl]SbF6 comprise relatively narrow asymmetric bands whose maxima are shifted to the red as the temperature is lowered: specifically λem(max) is 641 nm at r. t. (τ = 235 ns) and 676 nm at 77 K (τ = 1.36 μs). Temperature-dependent emission of this type is typical of a metal-metal-to-ligand charge transfer (MMLCT) excited state that has its origin in dz2 (Pt)-dz2 (Pt) orbital interactions in the crystal.

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Berdyugin, A. I., B. Tsim, P. Kumaravadivel, S. G. Xu, A. Ceferino, A. Knothe, R. Krishna Kumar et al. « Minibands in twisted bilayer graphene probed by magnetic focusing ». Science Advances 6, n^o 16 (avril 2020) : eaay7838. http://dx.doi.org/10.1126/sciadv.aay7838.

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Magnetic fields force ballistic electrons injected from a narrow contact to move along skipping orbits and form caustics. This leads to pronounced resistance peaks at nearby voltage probes as electrons are effectively focused inside them, a phenomenon known as magnetic focusing. This can be used not only for the demonstration of ballistic transport but also to study the electronic structure of metals. Here, we use magnetic focusing to probe narrowbands in graphene bilayers twisted at ~2°. Their minibands are found to support long-range ballistic transport limited at low temperatures by intrinsic electron-electron scattering. A voltage bias between the layers causes strong minivalley splitting and allows selective focusing for different minivalleys, which is of interest for using this degree of freedom in frequently discussed valleytronics.

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Omonov, Zafarjon. « Signs Of The Subjective Side Torture Of The Individual ». American Journal of Political Science Law and Criminology 03, n^o 03 (30 mars 2021) : 60–65. http://dx.doi.org/10.37547/tajpslc/volume03issue03-10.

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The article discusses the required and necessary elements of a crime, subjective symptoms mentioned in criminal legal norms, independent elements of torture, to be separate study, highlights the subjective aspect of torture, the behavior of persons, including illegal, its external (physical) and internal (mental) side, the processes in the psyche of the perpetrator, the act or omission, committed socially dangerous acts intentionally or negligently, the circumstances of guilt as mental attitudes, analyzes the circumstances of mental attitude as consisting of 1) smart time 2) the date of the will, 3) emotional, the differentiation of the two forms of guilt – deliberate and careless, differentiation of types of retaliation in volitional element, optional (proper retribution) or conscious conceded (twisted retribution), the motives and goals of torture, personal animosity.

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Martin, Joel L., et Josef Takats. « Trigonal prismatic versus octahedral coordination geometry of transition metal dithiolates : Comparison between saturated and unsaturated early transition metal tris(1,2-dithiolate) complexes ». Canadian Journal of Chemistry 67, n^o 11 (1 novembre 1989) : 1914–23. http://dx.doi.org/10.1139/v89-298.

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Reaction of a stoichiometric amount of H2edt/NaHedt (edt = ethane-1,2-dithiolate) with the appropriate metal amide, followed by cation exchange, gave the complexes [NEt4]2[M(edt)3] (M = Ti, 1; Hf, 2) and [AsPh4] [Nb(edt)3]•CH3CN, 3. The structure of 3 has been determined crystallographically (space group; cell dimensions; Z; unique data (I ≥ 3σ (I); R/Rw): [Formula: see text]; a = 9.095(1), b = 14.609(3), c = 15.639(3) Å and α = 60.09(2), β = 80.07(3), γ = 89.89(2)°; z = 2; 1488; 4.3/4.5. The coordination geometry of 3 is severely distorted from the trigonal prismatic (TP) structure found in the analogous Nb(1,2-S2C6H4)3−, which contains an unsaturated 1,2-dithiolate ligand system. The average twist angle between triangular faces is 33.3°. However, on the basis of VT 1H NMR spectroscopy it is argued that the TP form is at most 9–10 kcal mol−1 less stable than the observed geometry. A comparison between the structures of tris-chelate complexes of the early transition metals containing saturated and unsaturated 1,2-dithiolates and related ligands is made, and the factors thought to be responsible for TP vs. octahedral geometry are reviewed and their relative importance assessed. Keywords: structure, trigonal prismatic, 1,2-dithiolate, early transition metals.

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Al-Amiery, Ahmed A., Yasmien K. Al-Majedy, Haziem Abdulreazak et Hussain Abood. « Synthesis, Characterization, Theoretical Crystal Structure, and Antibacterial Activities of Some Transition Metal Complexes of the Thiosemicarbazone (Z)-2-(pyrrolidin-2-ylidene)hydrazinecarbothioamide ». Bioinorganic Chemistry and Applications 2011 (2011) : 1–6. http://dx.doi.org/10.1155/2011/483101.

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Problem Statement. In Iraq like most third world countries, attempts discovered new antibiotic drugs derived from thiosemicarbazide and its metal complexes and developed the branch of applied in organic chemistry.Approach. New (Z)-2-(pyrrolidin-2-ylidene)hydrazinecarbothioamide (L) was synthesized in a good yield by the reaction of pyrrolidone with thiosemicarbazide. Co(II), Ni(II), and Cu(II) complexes of (L) were prepared and characterized by FT-IR, UV/visible spectra,1HNMR, and CHN analyses. Moreover, charge, bond length, bond angle, twist angle, heat of formation, and steric energy were calculated by using of the ChemOffice program, and the DFT calculations for the complexes were done. The free ligand and its metal complexes were testedin vitroagainst several microorganisms (Staphylococcus aurous,E. coli,Proteus vulgaris,Pseudomonas, andKlebsiella pneumoniae) to assess their antimicrobial properties.Results. The study shows that these complexes have octahedral geometry; in addition, it has high activity against tested bacteria.Conclusion/Recommendations. Based on the reported results, it may be concluded that ligand acts as bidentate, neutral ligand, coordinating through one of the nitrogen and sulfur atoms.

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Cha, Won-Young, Jong Min Lim, Kyu Hyung Park, Masaaki Kitano, Atsuhiro Osuka et Dongho Kim. « Two modes of photoinduced twisted intramolecular charge transfer in meso-arylaminated subporphyrins ». Chem. Commun. 50, n^o 62 (2014) : 8491–94. http://dx.doi.org/10.1039/c4cc02368d.

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Photoinduced twisted intramolecular charge transfer (TICT) of meso-(4-dimethylamino)phenylamino subporphyrin 2 and meso-(4-nitro)phenylamino subporphyrin 3 has been revealed by steady-state and time-resolved absorption/fluorescence experiments and quantum calculations.

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He, Xiaolong, Xinyuan Zhang, Bifa Ji, Wenjiao Yao, Philip Lightfoot et Yongbing Tang. « Tilting and twisting in a novel perovzalate, K3NaMn(C2O4)3 ». Chemical Communications 57, n^o 20 (2021) : 2567–70. http://dx.doi.org/10.1039/d1cc00085c.

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A unique variant on the perovskite structure, K₃NaMn(C₂O₄)₃, has been identified with unconventional octahedral tilting, interpenetration of two topologically identical perovskite-like frameworks and an unusual, twisted oxalate ligand.

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Suzuki, Yuto, Norimitsu Tohnai, Akinori Saeki et Ichiro Hisaki. « Hydrogen-bonded organic frameworks of twisted polycyclic aromatic hydrocarbon ». Chemical Communications 56, n^o 87 (2020) : 13369–72. http://dx.doi.org/10.1039/d0cc06081j.

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Ruppel, Susanne, Christian Schulte to Brinke et F. Ekkehardt Hahn. « Synthesis and Coordination Chemistry of a Tris(benzene-o-dithiolato)- functionalized Ligand as a Siderophore Analog ». Zeitschrift für Naturforschung B 68, n^o 5-6 (1 juin 2013) : 551–56. http://dx.doi.org/10.5560/znb.2013-3069.

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As a siderophore analog, the tripodal tris(benzene-o-dithiol)-functionalized ligand H6-5, has been synthesized in four steps including the reaction of 1,3,5-(triaminomethyl)-2,4,6-triethylbenzene and 2,3-bis(isopropylmercapto)benzoyl chloride followed by removal of the S-protecting groups. Reaction of compound H6-5 with [Ti(OPr)4] in the presence of (NEt4)Cl leads to the formation of complex (NEt4)2[Ti(5)] featuring three bidentate benzene-o-dithiolato donors from one ligand coordinated to the metal center. An X-ray diffraction structure analysis with crystals of (NEt4)2[Ti(5)] DMF has shown that the coordination geometry at the metal center is best described as distorted trigonalprismatic with a twist angle of ϕav = 18:5°.

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Craig, DC, HA Goodwin et D. Onggo. « Steric Influences on the Ground State of Iron(II) in the Tris(3,3'-dimethyl-2,2'-bipyridine)Iron(II) Ion ». Australian Journal of Chemistry 41, n^o 8 (1988) : 1157. http://dx.doi.org/10.1071/ch9881157.

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The tris ( ligand ) complex ions of iron(II) and nickel(II) with 3,3′-dimethyl-2,2′-bipyridine (L) are described. Salts of [FeL3]2+ display anomalously temperature-dependent magnetic and spectroscopic properties which arise from a temperature-induced singlet (1A1) ↔ quintet (5T2) spin transition. The structures of [ML3][ClO4]2(M = Fe, Ni) have been determined and these reveal a strong twist (c. 37°) of the pyridine rings about the C-C bridge. This forces the metal atoms out of the bonding planes of the donor nitrogen atoms and effectively reduces the interaction between L and the metal atoms. The average M-N distances are 2.064 Ǻ (M = Fe) and 2.102 Ǻ (M = Ni). Crystal data: the two complex salts are isostructural in monoclinic space group C2/c. [FeL3][ClO4]2: a 12.252(8), b 15.568(5), c 19.288(11) Ǻ, β 93.62(3)°; Z 4; [NiL3][ClO4]2: a 12.255(5), b 15.619(4), c 19.419(9) Ǻ, β 93.23(2); Z 4.

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Thompson, Alexander M. W. Cargill, Stuart R. Batten, John C. Jeffery, Leigh H. Rees et Michael D. Ward. « Some Coordination Chemistry of the Bidentate Nitrogen-Donor Ligand 2-(2-Aminophenyl)pyridine ». Australian Journal of Chemistry 50, n^o 2 (1997) : 109. http://dx.doi.org/10.1071/c96146.

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Complexes of the chelating bidentate nitrogen-donor ligand 2-(2-aminophenyl)pyridine (L) are described. [PdL2] [PF6]2 (1) forms two types of crystal (1a,b) of which (1a) was crystallographically characterized [space group P 21/c a 10·974(6), b 14·757(4), c 8·223(2) Å; β 104·66(5)°; V 1288·3(8) Å3; Z 2]. It has a square-planar donor set about the metal, with the ligands mutually trans and with a twist of 35° between the pyridyl and phenyl rings. 1 H n.m.r. spectroscopy shows that pure (1a) and (1b) equilibrate in solution; it is likely that (1b) is thecis form of the complex. Electrochemical measurements on [Ru(bipy)2L] [PF6]2 (2) show that the RuII /RuIIIcouple is cathodically shifted by 0·34 V with respect to [Ru(bipy)3]2+ , indicating that replacing a pyridyl donor by an amine results in a significant increase of electron density on the metal centre: this effect is much larger with a primary amine ligand than with tertiary amines. The e.p.r. spectrum of [CuL2] [PF6]2 (3) shows that a small extent of association into a dinuclear complex occurs, a reaction which is solvent-dependent: addition of pyridine breaks up the dimer by coordination to the axial sites of the monomer, whose spectrum is characteristic of a tetragonal geometry (i.e. a planar array of two ligands L, and axial solvent molecules). Attempted recrystallization of other complexes of L from acetone afforded [C14H15N2] [PF6] (4), in which the free ligand L has condensed with acetone and then undergone an intramolecular cyclization by attack of the pyridyl nitrogen atom on the electrophilic carbon atom of the imine bond; this compound was also crystallographically characterized [space group P 21/n; a 8·258(2), b 10·036(4), c 17·976(7) Å; β 100·12(3)°; V 1466·8(10) Å3 ; Z 4]

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Kwan, Irene C. M., Yi-Min She et Gang Wu. « Nuclear magnetic resonance and mass spectrometry studies of 2′,3′,5′-O-triacetylguanosine self-assembly in the presence of alkaline earth metal ions (Ca2+, Sr2+, Ba2+) ». Canadian Journal of Chemistry 89, n^o 7 (juillet 2011) : 835–44. http://dx.doi.org/10.1139/v10-179.

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We report structural determination of cation-templated self-assembly of a guanosine derivative, 2′,3′,5′-O-triacetylguanosine (TAG), in the presence of three alkaline earth metal ions (Ca2+, Sr2+, and Ba2+) in CDCl3. Using a combination of nuclear magnetic resonance (NMR) and electrospray ionization mass spectrometry (ESI-MS) methods, we have found that TAG molecules form discrete octamers in the form of [TAG]8M2+ (M2+ = Ca2+, Sr2+, and Ba2+), which is composed of two G-quartets and a sandwiched metal ion. We have determined the ability of the three alkaline earth metal ions to promote TAG self-assembly (relative binding affinity) to be Sr2+ ≫ Ba2+ > Ca2+. More importantly, we have used two-dimensional (2D) NMR methods to determine the structural details of [TAG]8Sr2+. In particular, we found that each octamer consists of an all-anti G-quartet stacking on top of an all-syn G-quartet in a tail-to-head fashion with a twist angle of 45° between the two G-quartets. This TAG octamer structure represents a unique case quite different from other lipophilic guanosine octamers reported in the literature.

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Angeli, Mattia, et Allan H. MacDonald. « Γ valley transition metal dichalcogenide moiré bands ». Proceedings of the National Academy of Sciences 118, n^o 10 (3 mars 2021) : e2021826118. http://dx.doi.org/10.1073/pnas.2021826118.

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The valence band maxima of most group VI transition metal dichalcogenide thin films remain at the Γ point all of the way from bulk to bilayer. In this paper, we develop a continuum theory of the moiré minibands that are formed in the valence bands of Γ-valley homobilayers by a small relative twist. Our effective theory is benchmarked against large-scale ab initio electronic structure calculations that account for lattice relaxation. As a consequence of an emergent D6 symmetry, we find that low-energy Γ-valley moiré holes differ qualitatively from their K-valley counterparts addressed previously; in energetic order, the first three bands realize 1) a single-orbital model on a honeycomb lattice, 2) a two-orbital model on a honeycomb lattice, and 3) a single-orbital model on a kagome lattice.

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Meng, Weiying, Liyang Xie, Yu Zhang, Yawen Wang, Xiaofang Sun et Shijian Zhang. « Effect of Mean Stress on the Fatigue Life Prediction of Notched Fiber-Reinforced 2060 Al-Li Alloy Laminates under Spectrum Loading ». Advances in Materials Science and Engineering 2018 (6 juin 2018) : 1–16. http://dx.doi.org/10.1155/2018/5728174.

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This paper presents a study on the fatigue life prediction of notched fiber-reinforced 2060 Al-Li alloy laminates under spectrum loading by applying the constant life diagram. Firstly, a review on the state of the art of constant life diagram models for the life prediction of composite materials is given, which highlights the effect on the forecast accuracy. Then, the fatigue life of notched fiber-reinforced Al-Li alloy laminates (2/1 laminates and 3/2 laminates) is tested under cyclic stress, which has different stress cycle characteristics (constant amplitude loading and Mini-Twist spectrum loading). The introduced models are successfully realized based on the available experimental data of examined laminates. In the case of Mini-Twist spectrum loading, the effect of the constant life diagram on the life prediction accuracy of examined laminates is studied based on the rainflow-counting method and Miner damage criteria. The results show that the simple Goodman model and piecewise linear model have certain advantages compared to other complex models for the life prediction of notched fiber metal laminates with different structures under Mini-Twist loading. From the engineering perspective, the S-N curve prediction based on the piecewise linear model is most applicable and accurate among all the models.

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Digarbaeva, A. M., A. N. Kaliyeva, E. A. Kirshibayev et M. R. Bahtybaeva. « INFLUENCE OF HEAVY METALS ON THE DEVELOPMENT OF CORN VARIETIEShttps://doi.org/10.32014/2021.2518-1483.28 ». REPORTS 2, n^o 336 (13 avril 2021) : 39–45. http://dx.doi.org/10.32014/2021.2518-1483.28.

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Heavy metals are some of the most harmful chemicals in the environment today. Today, many scientists believe that the main factor that negatively affects the plant in saline conditions is the osmotic effect of salts. In conditions of soil salinity, the lack of plants causes dehydration of proteins, which negatively affects the physiological and biochemical processes of plants. Plants absorb heavy metals in different ways. It absorbs heavy metals from the soil through the roots and from the air through the stomata of the leaves, mainly through dust. The aim of the research is to study the influence of heavy metals on the physiological and biochemical processes of growth and development of maize varieties. The article presents the research results of the heavy metals influence on the elongation of seedlings and the synthesis of photosynthetic pigments during the germination of maize varieties. It is obvious that heavy metals affect the growth and plant development from the initial germination stage of corn kernels. The results of monitoring various effects of heavy metals on photosynthetic pigments are also presented. In addition, the length of the above- water and underground parts of the biomass, the ratio of dry weight to actual weight is the heavy metals effect on plants. For example, the leaves turned dark green, the stems twisted, did not fully open and turned pink. Under the influence of heavy metals, plant development, metabolism and photosynthesis are disrupted, as well as the normal course of respiration and photosynthesis. According to the results obtained, the impact of heavy metals on maize varieties significantly inhibits the accumulation and growth of biomass. In particular, the processes of plant root growth are suppressed. Differences in the tolerance of different varieties of heavy metals can be explained by their varietal characteristics and genetic basis. Currently, there is a theoretical and practical interest in the identification of ion-resistant forms of heavy metals, their ability to detect and reveal their nature, the development of ways to increase the impact and resistance of heavy metals on plants. Formulating the results of the study, it was found that different heavy metals concentrations (CuSO4 and CdSO4) negatively affect the growth of corn varieties. This can be seen from the tables below (tables 1, 2, 3, 4).

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Rahman, Md, Jonathan Buchspies et Michal Szostak. « N-Acylphthalimides : Efficient Acyl Coupling Reagents in Suzuki–Miyaura Cross-Coupling by N–C Cleavage Catalyzed by Pd–PEPPSI Precatalysts ». Catalysts 9, n^o 2 (1 février 2019) : 129. http://dx.doi.org/10.3390/catal9020129.

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We report a general, highly selective method for Suzuki–Miyaura cross-coupling of N-acylphthalimides via N–C(O) acyl cleavage catalyzed by Pd–PEPPSI-type precatalysts. Of broad synthetic interest, the method introduces N-acylphthalimides as new, bench-stable, highly reactive, twist-controlled, amide-based precursors to acyl-metal intermediates. The reaction delivers functionalized biaryl ketones by acylative Suzuki–Miyaura cross-coupling with readily available boronic acids. Studies demonstrate that cheap, easily prepared, and broadly applicable Pd–PEPPSI-type precatalysts supported by a sterically demanding IPr (1,3-Bis-(2,6-diisopropylphenyl)imidazol-2-ylidene) ancillary ligand provide high yields in this reaction. Preliminary selectivity studies and the effect of Pd–N-heterocyclic carbenes (NHC) complexes with allyl-type throw-away ligands are described. We expect that N-acylphthalimides will find significant use as amide-based acyl coupling reagents and cross-coupling precursors to acyl-metal intermediates.

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Begel, Svetlana, Ralph Puchta et Rudi van Eldik. « Host–guest complexes of mixed glycol-bipyridine cryptands : prediction of ion selectivity by quantum chemical calculations, part V ». Beilstein Journal of Organic Chemistry 9 (27 juin 2013) : 1252–68. http://dx.doi.org/10.3762/bjoc.9.142.

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The selectivity of the cryptands [2.2.bpy] and [2.bpy.bpy] for the endohedral complexation of alkali, alkaline-earth and earth metal ions was predicted on the basis of the DFT (B3LYP/LANL2DZp) calculated structures and complex-formation energies. The cavity size in both cryptands lay between that for [2.2.2] and [bpy.bpy.bpy], such that the complexation of K+, Sr2+ and Tl3+ is most favorable. While the [2.2.bpy] is moderately larger, preferring Rb+ complexation and demonstrating equal priority for Sr2+ and Ba2+, the slightly smaller [2.bpy.bpy] yields more stable cryptates with Na+ and Ca2+. Although the CH2-units containing molecular bars fixed at the bridgehead nitrogen atoms determine the flexibility of the cryptands, the twist angles associated with the bipyridine and glycol building blocks also contribute considerably.

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Lee, Dong Hun, et Myung-Hyun Lee. « Gapped Surface Plasmon Polariton Waveguide Device Based on a Liquid Crystal ». Journal of Nanoscience and Nanotechnology 15, n^o 10 (1 octobre 2015) : 7711–16. http://dx.doi.org/10.1166/jnn.2015.11175.

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We propose a gapped surface plasmon polariton waveguide (G-SPPW) device based on a liquid crystal (LC) at a wavelength of 1.55 μm. The G-SPPW device is composed of an input 2.0-μm-wide and 5.0-μm-long insulator-metal-insulator waveguide (IMI-W), an 8-μm-long gap, and an output 2.0-μm-wide and 25.0-μm-long IMI-W. The LC is used for the gap and the 5.15-μm-thick upper and lower dielectric layers. The input surface plasmon polaritons (SPPs) propagate and jump over the gap in the G-SPPW with a coupling loss of less than ∼0.68 dB. The propagation and coupling losses of the 38-μm-long G-SPPW device are varied in the range of ∼0.5268 dB to ∼2.6716 dB and ∼0.1446 dB to ∼0.6784 dB, respectively, with LC tilt angles (1, 2) = 0° ∼ 90° at a fixed 90° twist angle. The normalized transmission of the G-SPPW device is also varied in the range from −3.351 dB to −0.6714 dB with 1, 2 = 0° ∼ 90° at a fixed 90° twist angle. The output SPP characteristics of the G-SPPW device can be properly controlled by the orientation of the LC molecules. The proposed G-SPPW device shows potential for new active plasmonic device applications.

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Dong, ZhiLi, et T. J. White. « Calcium–lead fluoro-vanadinite apatites. II. Equilibrium structures ». Acta Crystallographica Section B Structural Science 60, n^o 2 (18 mars 2004) : 146–54. http://dx.doi.org/10.1107/s0108768104001843.

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The synthetic vanadinites (Pb x Ca10−x )(VO4)6(F1−2y O y □ y )2, 0.57 < x < 9 and 0.10 < y < 0.47, adopt the P63/m apatite structure with 9.7835 (3) ≤ a ≤ 10.0531 (1) Å and 7.0318 (2) ≤ c ≤ 7.3033 (1) Å. The calcium endmember is monoclinic, space group P21/m, with a = 9.7370 (3), b = 9.7358 (4), c = 7.00572 (9) Å, γ = 120.002 (5)°. For mixed metal compounds (x ≠ 0) the partitioning of calcium and lead over the A I(4f) and A II(6h) positions is nonstoichiometric, with lead preferentially favouring the larger A II site at a partitioning coefficient k Pb(A I/A II) ≃ 0.33 for all x < 7. A miscibility gap exists for 2 < x < 3. Trends in crystallographic parameters can be correlated through consideration of the A IO6 metaprism twist angle (φ) that can be used to derive ideal cell parameters from triangular anion networks.

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Bock, Hans, Sabine Nick, Christian Näther et Jan W. Bats. « Strukturen ladungsgestörter Moleküle, 47 [1 , 2 ] Dinatrium- und Dikalium-Nitranilate : Die Cyanin-Verzerrung der Kohlenstoff-Sechsringe / Structures of Charge-Perturbed Molecules 47 [1,2] Disodium and Dipotassium Nitranilates : The Cyanine Distortion of the Six-Membered Carbon Ring ». Zeitschrift für Naturforschung B 49, n^o 8 (1 août 1994) : 1021–30. http://dx.doi.org/10.1515/znb-1994-0803.

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Crystals of lemon yellow dipotassium nitranilate and of yellow disodium nitranilate dihydrate have been grown and their structures determined at 290 and 200 K. The six-member- ed, O2N-disubstituted rings show a pronounced cyanine distortion with all four CO bonds identical and the two (OCC(NO2)CO)⊖ chains connected by single CC bonds of each 156 pm length. In the anhydrous K⊕ salt, the ring is planar, but in the Na⊕ hydrate salt it exhibits a twist conformation. Quantum chemical calculations allow to reproduce the structure in every detail, demonstrate strong charge alternation along the cyanine chains with considerable delocalization into the O2N acceptor substituents, and suggest that the rather long connecting CC bonds contain positively charged carbon centers on both ends. In addition, metal ion coordination effects as well as the rather high pKa value of nitranilic acid are rationalized.

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Barkhudaryan, Vigen G., Gayane V. Ananyan, Yeva B. Dalyan et Samvel G. Haroutiunian. « Development of viscometric methods for studying the interaction of various porphyrins with DNA. Part I : meso-tetra-(4N-hydroxyethylpyridyl) porphyrin and its Ni-, Cu-, Co- and Zn- containing derivatives ». Journal of Porphyrins and Phthalocyanines 18, n^o 07 (juillet 2014) : 594–99. http://dx.doi.org/10.1142/s1088424614500357.

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The influence of water soluble cationic meso-tetra(4N-hydroxyethyl)pyridyl porphyrin ( H 2 THOEtPyP 4) and it's metal complexes with Ni ( II ), Cu ( II ), Co ( II ) and Zn ( II ) on hydrodynamic and spectral behavior of DNA solutions has been studied by viscometry and UV-vis absorption methods. It was shown that the presence of planar porphyrins, such as H 2 THOEtPyP 4, NiTHOEtPyP 4 and CuTHOEtPyP 4 leads to an increase in viscosity at relatively small concentrations, and then decreases to stable values. Such behavior corresponds to intercalation of these porphyrins in DNA structure, which results in a decrease of helical twist and lengthening of the DNA molecule. In the case of porphyrins with axial ligands, such as ZnTHOEtPyP 4 and CoTHOEtPyP 4, the relative viscosity decreases, which is explained by self-stacking of these porphyrins on DNA surface. Calculation and interpretation of binding parameters (Kb and n) demonstrated good agreement of viscometric and spectrophotometric measurements.

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Cole, Jacqueline M., Michael C. W. Chan, Vernon C. Gibson et Judith A. K. Howard. « Effects of the [OC6F5] moiety upon structural geometry : crystal structures of half-sandwich tantalum(V) aryloxide complexes from reaction of Cp*Ta(N t Bu)(CH2 R)2 with pentafluorophenol ». Acta Crystallographica Section B Structural Science 67, n^o 5 (31 août 2011) : 416–24. http://dx.doi.org/10.1107/s0108768111029259.

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The synthesis, chemical and structural characterization of a series of pentamethylcyclopentadienyl (Cp*) tantalum imido complexes and aryloxide derivatives are presented. Specifically, the imido complexes Cp*Ta(N t Bu)(CH2 R)2, where R = Ph [dibenzyl(tert-butylamido) (η5-pentamethylcyclopentadienyl)tantalum(IV) (1)], Me2Ph [tert-butylamido)bis(2-methyl-2-phenylpropyl) (η5-pentamethylcyclopentadienyl)tantalum(IV) (2)], CMe3 [(tert-butylamido)bis(2,2-dimethylpropyl) (η5-pentamethylcyclopentadienyl)tantalum(IV) (3)], are reported. The crystal structure of (3) reveals α-agostic interactions with the Ta atom. The resulting increase in the tantalum core coordination improves electronic stability. As such it does not react with pentafluorophenol, in contrast to the other two reported imido complexes [(1) and (2)]. Addition of C6F5OH to (1) yields a dimeric aryl-oxide derivative, [Cp*Ta(CH2Ph)(OC6H5)(μ-O)]2 [di-μ-oxido-bis[benzyl(pentafluorophenolato) (η5-pentamethylcyclopentadienyl)tantalum(V)] (4)]. Its crystal structure reveals long Ta—O(C6H5) bonds but short oxo-bridging Ta—O bonds. This is explained by accounting for the fierce electronic competition for the vacant d π orbitals of the electrophilic TaV centre. Steric congestion around each metal is alleviated by a large twist angle (77.1°) between the benzyl and pentafluorophenyl ligands and the ordering of each of these groups into stacked pairs. The imido complex (2) reacts with C6F5OH to produce a mixture of Cp*Ta(OC6F5)4 [tetrakis(pentafluorophenolato)(η5-pentamethylcyclopentadienyl)tantalum(V) (5)] and [Cp*Ta(OC6F5)2(μ-O)]2 [di-μ-oxido-bis[bis(pentafluorophenolato)(η5-pentamethylcyclopentadienyl)tantalum(V)] (6)]. Steric congestion is offset in both cases by the twisting of its pentafluorophenyl ligands. Particularly strong electronic competition for the empty d π metal orbitals in (6) is reflected in its bond geometry, and owes itself to the more numerous electron-withdrawing pentafluorophenyl ligands. The balance of steric and electronic factors affecting the reactivity of Cp* tantalum imido based complexes with pentafluorophenol is therefore addressed.

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Clegg, William, Ross W. Harrington, Kazem Barati, Mohammad Hossein Habibi, Morteza Montazerozohori et Arash Lalegani. « Synthesis, characterization and crystal structures of the bidentate Schiff baseN,N′-bis(2-nitrocinnamaldehyde)ethylenediamine and its complex with CuNCS and triphenylphosphane ». Acta Crystallographica Section C Structural Chemistry 71, n^o 7 (18 juin 2015) : 578–83. http://dx.doi.org/10.1107/s2053229615010815.

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Reaction of copper(I) thiocyanate and triphenylphosphane with the bidentate Schiff baseN,N′-bis(trans-2-nitrocinnamaldehyde)ethylenediamine {Nca2en, (1); systematic name (1E,1′E,2E,2′E)-N,N′-(ethane-1,2-diyl)bis[3-(2-nitrophenyl)prop-2-en-1-imine]}, C20H18N4O4, in a 1:1:1 molar ratio in acetonitrile resulted in the formation of the complex {(1E,1′E,2E,2′E)-N,N′-(ethane-1,2-diyl)bis[3-(2-nitrophenyl)prop-2-en-1-imine]-κ2N,N′}(thiocyanato-κN)(triphenylphosphane-κP)copper(I)], [Cu(NCS)(C20H18N4O4)(C18H15P)] or [Cu(NCS)(Nca2en)(PPh3)], (2). The Schiff base and copper(I) complex have been characterized by elemental analyses, IR, electronic and1H NMR spectroscopy, and X-ray crystallography [from synchrotron data for (1)]. The molecule of (1) lies on a crystallographic inversion centre, with atransconformation for the ethylenediamine unit, and displays significant twists from coplanarity of its nitro group, aromatic ring, conjugated chain and especially ethylenediamine segments. It acts as a bidentate ligand coordinatingviathe imine N atoms to the CuIatom in complex (2), in which the ethylenediamine unit necessarily adopts a somewhat flattenedgaucheconformation, resulting in a rather bowed shape overall for the ligand. The NCS−ligand is coordinated through its N atom. The geometry around the CuIatom is distorted tetrahedral, with a small N—Cu—N bite angle of 81.56 (12)° and an enlarged opposite angle of 117.29 (9)° for SCN—Cu—P. Comparisons are made with the analogous Schiff base having no nitro substituents and with metal complexes of both ligands.

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