Vol 57, No 8 (2016)

A theoretical description of the relaxation kinetics of photoexcited states in chains of exchange clusters is developed in the mean-field approximation. It is found that in contrast to the analog of this phenomenon in the light-induced electron spin-state trapping (LIESST) effect well known for the conventional spin crossover compounds of Fe(II), the relaxation kinetics in chains of exchange clusters can be self-decelerating due to the different relaxation rates of two types of photoexcited states in the chain. The proposed theoretical approach qualitatively explains the experimentally observed difference in relaxation kinetics at different initial excitation intensities of the system during photoexcitation of breathing crystal compounds.

The electronic structure and lattice parameters of several quasi-one-dimensional compounds–known VS₄, NbCl₄, and NbS₃ and hypothetical NbS₄ and VS₃–are obtained using density functional theory. Comparative analysis of chemical bonding and charge distribution in all these compounds reveals the possible origin of the structural instability of NbS₄ and VS₃.

Novel transition metal complexes with the repaglinide ligand [2-ethoxy-4-[N-[1-(2piperidinophenyl)-3-methyl-1-1butyl] aminocarbonylmethyl]benzoic acid] (HL) are prepared from chloride salts of manganese(II), iron(III), copper(II), and zinc(II) ions in water-alcoholic media. The mononuclear and non-electrolyte [M(L)₂(H₂O)₂]•nH₂O (M = Mn²⁺, n = 2, M = Cu²⁺, n = 5 and M = Zn²⁺, n = 1) and [M(L)₂(H₂O)(OH)]•H₂O (M = Fe³⁺) complexes are obtained with the metal:ligand ratio of 1:2 and the L-deprotonated form of repaglinide. They are characterized using the elemental and molar conductance. The infrared, ¹H and ¹³C NMR spectra show the coordination mode of the metal ions to the repaglinide ligand. Magnetic susceptibility measurements and electronic spectra confirm the octahedral geometry around the metal center. The experimental values of FT-IR, ¹H, NMR, and electronic spectra are compared with theoretical data obtained by the density functional theory (DFT) using the B3LYP method with the LANL2DZ basis set. Analytical and spectral results suggest that the HL ligand is coordinated to the metal ions via two oxygen atoms of the ethoxy and carboxyl groups. The structural parameters of the optimized geometries of the ligand and the studied complexes are evaluated by theoretical calculations. The order of complexation energies for the obtained structures is as follows:

\(Fe(III) complex < Cu(II) complex < Zn(II) complex < Mn(II) complex.\)

A comparative study of the band structure and magnetic properties of the hexagonal and cubic modifications of aluminum nitride doped with boron, carbon, and oxygen in the nitrogen sublattice has been performed using the ab initio FLAPW-GGA method. Preliminary conclusions on the comparative chemical activity of these phases are drawn from estimates for the energies of substitution of nitrogen atoms by dopants. It has been shown that the doping with boron and nitrogen leads to transition of hexagonal AlN into a magnetic state with high spin polarization of near-Fermi electrons, but for cubic AlN, this effect is absent.

The title compound is synthesized from the precursors 1,2-diaminobenzene and 2,2′-bipyridine-4,4′-dicarboxylic acid (dcbpy) and characterized using ESI-Mass, ¹H NMR, FT-IR and single crystal X-ray analysis. We are the first to report the crystal structure of the 4,4′-bis(benzimidazolyl)-2,2′-bipyridine (bimbpy) ligand. The photophysical properties of the compound in dimethyl sulfoxide and in the aqueous medium are studied. The interaction studies of bimbpy with bovine serum albumin (BSA) were performed with the fluorescence technique and it strongly binds with BSA.

The chlorobenzene (CB)–o-dichlorobenzene (o-DCB) liquid system has been studied by classical molecular dynamics simulation over the entire range of concentrations. The structure of the solutions is characterized by using radial angular distribution functions for the distances between the planes of benzene rings and the angle between them, using radial distribution functions for the distances between chlorine atoms, and by calculating the self-diffusion coefficients and local dipole moments. Halogen aggregation in the pure components and solutions is analyzed. It is found that in pure CB, chlorine aggregates consisting of four to ten molecules are most likely to form. The sizes of chlorine aggregates increase with increasing o-DCB concentration, and at a o-DCB concentration of 0.50-1.00 ppm, an extended system of chlorine–chlorine contacts is formed. In pure o-DCB, the chlorine aggregation system includes 99% of the molecules of the simulated system. The agglomeration of solute molecules in the range of dilute solutions (x < 0.1 ppm) is investigated.

Crystal structures of newly synthesized tetramethylammonium hexafluoridoniobate(V) and hexafluoridotantalate(V) (CH₃)₄N[МF₆] (M=Nb, Ta) have been determined; they crystallize in the tetragonal crystal system, sp. gr. P4/nmm. Crystal structures of isostructural compounds (CH₃)₄N[МF₆] (M=Nb, Ta) are formed by virtually regular tetrahedral tetramethylammonium cations (CH₃)₄N⁺ (NMe₄, TMA) and octahedral complex anions [МF₆]^– (M=Nb, Ta), fluorine atoms of the equatorial plane are statistically disordered over two positions. Ionic interactions and weak hydrogen bonds C–H•••F join the cations and the complex anions in a 3D assembly.

A series of six-coordinated Ni(II) complexes, with the general formula Ni(Xan)L₂ (where Xan = = isoamyldithiocarbonato and L = 2-bromopyridine, 3-bromopyridine, 4-acetylpyridine, 3-hydroxypyridine and 2-methoxypyridine) are synthesized and characterized by the elemental analysis and various physicochemical techniques such as magnetic susceptibility and conductivity measurements, UV-visible and infrared spectral data. Based on the electronic spectra and magnetic susceptibility measurements, an octahedral geometry is proposed for all the complexes. IR spectral data show that in all these complexes substituted pyridines coordinate to the metal ion through nitrogen atoms occupying the fifth and sixth axial positions, whereas O-alkyldithiocarbonate acts as a monoanion bidentate ligand and occupies the planar positions of octahedral structures. The structure of the adduct with 3-bromopyridine is elucidated by the single crystal X-ray diffraction method. The complex crystallizes in the triclinic space group P-1 with unit cell parameters a = 6.5855(4) Å, b = 9.4984(6) Å, c = 12.4518(8) Å, α = 87.944(5)°, β = 78.843(5)°, γ = 77.794(5)°. The crystal structure of the molecule is stabilized by intermolecular C–H…S and C–H…π interactions.

Double complex salts (DCS) α-[Pd(NH₃)₄][IrF₆]·H₂O (P2₁/m, a = 6.3181(3) Å, b = 10.8718(5) Å, с = 7.4526(4) Å, β = 103.568(2)°), β-[Pd(NH₃)₄][IrF₆]·H₂O (P2₁/с, a = 8.5773(3) Å, b = 10.8791(4) Å, с = = 12.6741(3) Å, β = 122.497(2)°), [Pd(NH₃)₄]₃[IrF₆]₂Cl₂·H₂O (P-1, a = 7.6080(2) Å, b = 7.6274(2) Å, с = 11.8070(3) Å, β = 122.497(2)°), and [Pd(NH₃)₄]₂[IrF₆]NO₃ (Fm-3m, a = 11.21210(10) Å) have been synthesized and structurally characterized for the first time. The existence of polymorphs for the DCS has been revealed. The influence of the chemical composition of the initial reagents on the reaction course and, respectively, the products, has been demonstrated. A hypothesis on the influence of the second coordination sphere on the formation of one or the other polymorph of the DCS has been suggested. It has been shown that the series α-[Pd(NH₃)₄][МF₆]·H₂O (M = Pt, Pd) exhibits isostructurality.

Indoline alkaloids kopsinilam and kopsinine extracted from the plant Vinca erecta have been studied by X-ray crystallography; mono and double salts of the latter alkaloid also have been examined. Experimentally determined positions of Н atoms suggest sp³ hybridization of the indoline nitrogen atom N1 in the bases and the salts. Tetrahedral hybridization of the atom N1 in indoline alkaloids favors the formation of their double salts, what is unlikely for indole and indolinine alkaloids. In the halogen double salts there is an intramolecular Н bond between one of the protons of the NH₂ group and the oxygen of the methoxycarbonyl group, that is absent in the mono salts and pure bases.

Interpretation of X-ray photoelectron spectra (XPS) for p-nitroaniline and the nitroxide radical was carried out by the time-dependent density functional theory (TD-DFT) method using the (Z+1)^N–1 approximation. Consideration of satellite transitions in the interpretation of the XPS spectra leads to good agreement with experiment. The shape of the X-ray photoelectron spectra of the radicals mainly depends on the relaxation processes caused by the X-ray hole screening effect and leading to the formation of satellite lines. The structure of the satellites in the XPS spectra depends on the spin state of the system and intermolecular interaction.

α-³⁴S has been studied with X-ray crystallography within 100–363 K. Anisotropy of the evolution of the parameters of the orthorhombic unit cell has been examined. The absolute increase in the cell volume is 154 ų, and the relative one is 4.8%. It has been demonstrated that in the studied range the intramolecular S–S bond lengths are shortened at average by 0.006 Å on heating. At the same time, intermolecular contacts S…S shorter than the sum of van der Waals radii demonstrate average elongation of 0.097 Å.

Coordination nickel pyrophosphate [Ni(H₂P₂O₇)(C₁₂H₈N₂)₂]•2.5H₂O (I) is hydrothermally synthesized and characterized by single crystal X-ray diffraction. The title compound crystallizes in the triclinic system, space group P-1, with cell parameters M = 640.07, a = 10.285(2) Å, b = 10.510(3) Å, c = 12.775(3) Å, α = 88.06(2)°, β = 77.87(2)°, γ = 89.26(2)°, V = 1349.2(5) ų, Z = 2, R₁[I > 2σ(I)] = 0.0438, wR₂[I > > 2σ(I)] = 0.1244. This compound displays a new structure of ladder-like 2D layers parallel to (010) consisting of [Ni(H₂P₂O₇)(phen)₂] entities with the distorted octahedral NiN₄O₂ coordination geometry arising from two chelating 1,10-phenanthroline ligands and diphosphate [H₂P₂O₇] ligand bridged through π•••π stacking interactions between the neighboring 1,10-phen ligands with interplanar distances of 4.425 Å and 4.525 Å. In the compound, the phen ligands bind in a bidentate fashion to the metal atoms and the ladder-like structure of the compound extends into a three-dimensional supramolecular array via hydrogen bonds (O4–H17…O5) between diphosphate groups, which delimits b axis tunnels where water molecules are located.

The newly attempted template synthesis involving 1-hydrazinocarbonylmethyl-7-bromo-5-phenyl-1,2-dihydro-3H-1,4-benzdiazepin-2-one (Hydazepam–HHy) (1), 2-hydroxy-1-naphtaldehyde (HNf) (2) and tin tetrachloride (3) in the solution of iso-propanol has afforded a tin(IV) coordination compound with 1-[(2-hydroxy-1-naphtyl)methylenhydrazino]carbonylmethyl-7-bromo-5-phenyl-1,2-dihydro-3H-1,4-benzdiazepin-2-one (H₂HyNf) (4)–the product of condensation of 1 with 2. The composition of the complex [Sn(HHyNf)Cl₃] (5) and its structure have been confirmed by a number of physical chemical methods. Its molecular structure has been determined by single crystal XRD. The coordination polyhedron of the tin atom is an octahedron formed by three chlorine atoms, azomethine nitrogen atom and two oxygen atoms of the carbonyl and deprotonated hydroxy group of the ligand.

The structures of two novel 8-hydroxyquinoline derivatives with 1,3-tropolonic fragment in the second position of the quinoline ring have been studied as a promising new multidentate system with extended coordination capabilities.