Vol 60, No 3 (2019)

The paper reviews literature data on the structural features of coordination compounds based on spacer-armed pyridylazoles (pyrazoles, 1,2,4- and 1,2,3-triazoles, tetrazoles). It is shown that the realization of the “maximum site occupancy” (MSO) principle for the metal:ligand ratio of 2:3 leads to the self-assembly of polynuclear clusters, their metal cores having highly symmetric architectures of tetrahedron, trigonal prism, cube, truncated tetrahedron, and cuboctahedron.

The paper presents a theoretical DFT UB3LYP/6-311++G(d,p) modeling of the structure and magnetic properties of Cu(II) coordination compounds with tridentate Schiff bases derived from 2-tosylaminobenzaldehyde and amino alcohols. It is shown that the elongation of the aliphatic chain in the amine part of ligand systems prevents the formation of binuclear metal-chelate structures. At the same time, mononuclear bis-chelate complexes, as well as mono-adducts containing a coordinated solvent molecule and a tridentate azomethine compound, are formed regardless of the number of methylene units.

The potential energy surface of 2-oxo-1,2,3,4-tetrahydropyrimidines (THPMs) is explored by density functional theory at the B3LYP level with a 6-31++G** basis set. All minimum and maximum points display a flat boat conformation of the heterocyclic ring in which the C₄-aryl ring occupies a pseudo-axial position. In order to elucidate the comparative effect of the space orientation of the C₄-aryl ring or the 5-CO group towards the heterocyclic ring on the total energy content of THPM and also the changes in some characteristic bond lengths and angles, these groups are rotated around the C₄-Cn and C₅-C₇ single bonds, respectively. The results indicate an effect of the orientation of the 5-CO group on the investigated parameters compared to that of the C₄-aryl ring. Natural bond orbital (NBO) analysis is carried out to investigate the effect of various intramolecular interactions and also intermolecular interactions with a medium in the calculation on the stabilization energy compared to those in the gas phase calculation. The results indicate that the dipole moments and also the charge densities on the specific atoms are effectively changed by the orientation of the C4-aryl ring and the 5-CO group towards the heterocyclic ring. In addition, bond rotations around the C₄-Cn and C₅-C₇ single bonds in the oxidized compounds 2-oxo-1,2-dihydropyrimidines (DHPMs) are also carried out to compare the effects of these changes with those in THPMs.

In this work, Raman spectra are recorded for the crystals of compounds containing N-H⋯N hydrogen bonds demonstrating proton tautomerism. The spectra are obtained in the temperature range of 5–300 K. The starting temperature of proton tunneling on the bonds is determined from the temperature dependence of peak positions of translational vibrations N⋯N participating in hydrogen bonding. The beginning of proton ordering is found from the half-width temperature dependence. Both parameters of proton tautomerism correlate with the type and strength of the hydrogen bond.

This work aims at studying the influence of structural parameters on computations of the ⁹³Nb quadrupolar interaction and chemical shift parameters in various niobates using first-principles approaches. We demonstrate that some of the computed NMR parameters, especially the isotropic chemical shift and the quadrupolar coupling constant, may differ either the X-ray crystal structure or a relaxed structure used for the calculation of the spectroscopic properties.

Analytical expressions for the dynamic specific conductance coefficient σ(ω) and the dynamic electroelasticity modulus ∊(ω) are obtained by solving kinetic equations using specific expressions for the potential energy Φ_ab(r) of the interaction between structural units of the solution and the equilibrium radial distribution function g_ab(r). Friction coefficients β_a and β_b are calculated numerically; relaxation times τ_a, τ_b, τ_ab along with ∊(ω) and σ(ω) values are determined for aqueous solutions of LiCl, NaCl, KCl, and CsCl as functions of the concentration c, density ρ, and temperature T in a wide frequency range ω. The obtained theoretical data are presented in the form of tables and graphs and are compared with experimental results show a satisfactory agreement between them.

The structures of chalcogenides where some large S²⁻, Se²⁻, Te²⁻ anions are closely surrounded by 6–12 Cu⁺ or Ag⁺ cations in 3–4 coordination are considered. These compact (X²⁻M_n⁺) groups, being the anion-centered clusters (ACCs), can be thought as highly charged voluminous analogues of large K, Rb, T1^(I), Cs cations. Together they perform related structural functions.

A cobalt coordination polymer with the formula {[Co(bipmo)(bpa)]_n · H₂O}_n(1) (bipmo = = bis(4-(1H-imidazol-1-yl)phenyl)methanone, H₂bpa = 1,1′-biphenyl-2,2′-dicarboxylic acid) is synthesized and structurally characterized. The single crystal X-ray diffraction analysis shows that the coordination geometry of the Co(II) ion is a quite distorted octahedron. The Co1 atom is octahedrally coordinated by four O atoms from two bpa²⁻ ligands, and two N atoms from two bipmo ligands. Interestingly, adjacent Co ions are linked by bpa²⁻ bridges to generate an infinite one-dimensional coordination chain along the b axis, which are further connected by bipmo to generate two-dimension layers parallel to the (1 0 1) plane. The thermal stability of the complex are also investigated.

A crystalline mixed-metal sulfate compound NaPr(SO₄)₂(H₂O) is synthesized under hydrothermal conditions and thoroughly characterized. Sodium bisulfite (NaHSO₃) and piperazine are used with praseodymium acetate to obtain this sulfate-based structure. The single crystal structural analysis shows that the compound has the NaCe(SO₄)₂ · H₂O structure type and crystallizes in the trigonal space group P3₂21 (No. 154) with a = 6.9872(2) Å, c = 12.8935(8) Å, and V = 545.14(4) ų. The compound has three-dimensional connectivity formed by the sulfate units with Pr and Na centers. Tricapped trigonal prismatic PrO₉ units and square-antiprismatic NaO₈ units link to the SO₄ tetrahedron for building the three-dimensional structure. The compound is also characterized by PXRD, TGA, and FT-IR spectroscopy. The present study illustrates the usefulness of the bisulfite anion and secondary amine for the chiral structure building.

We describe the results of the X-ray diffraction study of a dysprosium(III) complex with trihydrazone of 3-methyl-1-phenyl-4-formylpyrazole-5-one and 1,3,5-benzenetricarboxylic acid, as well as a heteroligand gadolinium(III) complex with tri- and dihydrazone of 3-methyl-1-phenyl-4-formylpyrazole-5-one and 1,3,5-benzenetricarboxylic acid (H₃L and H3L¹ respectively). It is determined that the homoligand complex of dysprosium has a M₄L₄ composition and a pseudotetrahedral structure in which metal ions occupy vertices of a trigonal pyramid and trinucleating ligands are located on its sides. The heteroligand gadolinium complex Gd₃(L)(HL¹)₃ has a trigonal structure. Metal ions at the triangle vertices are linked by a trinucleating ligand located above the triangle plane, and three binucleating ligands link the central atoms in pairs. The geometry of dysprosium and gadolinium coordination polyhedra correspond to a three-capped trigonal prism.