Vol 60, No 11 (2019)

Spatial and electronic structures of three-coordinated silicon molecules are calculated within MP2/6-311G(2d,p) and HF/6-311++G(3df,3pd) methods using the PC GAMESS-Firefly software package. AIM and NBO methods are used to determine main characteristics of silicon-substituent bonds in these molecules. Topologically, Si-C, Si-N, Si-Cl, and Si-O bonds may be characterized as “intermediate” bonds, and Si-Si bonds are characterized as covalent bonds.

The prediction of the nature of a reactivity descriptor is of paramount importance to theoretical chemists and thus, much work has been carried out in this area. The electrophilicity index (ω), an important theoretical construct of chemistry, is a measure of the electron acceptor affinity to gain an additional electronic charge from the environment. It is quantified in terms of the maximum energy stabilization in species, which arises due to accepting a charge. The electrophilicity concept is being extensively used in modern chemistry, although the finest measurement scale of the electrophilicity index is yet to be designed. In this study, a new scale of the electrophilicity index invoking the force concept based on the effective nuclear charge (Z_eff) and absolute atomic radii (r) is proposed for 97 elements of the periodic table, which is determined through the regression analysis. The computed data follows the periodicity very well satisfying the sine qua non of the standard scale of the electrophilicity index. The electrophilicity equalization principle is also established in terms of the computed data. To test the model in the real field, the internuclear bond distance of some molecules is calculated in terms of the computed electrophilicity index. A comparative study of the theoretical vis-à-vis experimental internuclear bond distance reveals the efficacy of the proposed scale.

The para-substituent effect on the acidity strength of boronic acid (para-C₆H₄XB(OH)₂; X = NMe₂, NH₂, OMe, H, F, Cl, CHO, COOH, NO₂) is explored at the B3LYP*/6-31+G(d, p) level of theory in an aqueous solution. The conductor-like polarized continuum model (CPCM) is used for the calculation in the aqueous phase. The CPCM calculations are performed with the SMD-Coulomb atomic radii. Then, the pK_a values corresponding to these molecules are calculated in an aqueous solution. Atomic charges of the acidic proton are calculated with QTAIM, APT, and Mulliken methods. A linear correlation between the calculated pK_a values with the Hammett constant, deprotonating energy, and atomic charges of acidic proton are analyzed.

Spatial and electronic structures of various zinc(II) coordination compounds containing different L-histidine forms are quantum-chemically calculated with the HyperChem 8.0 software taking into account the effect of the solvent (water). Geometry optimization is performed by molecular mechanics, the semiempirical MNDO/d method, and the Polak-Ribière nonlinear conjugate gradient method. Molecular geometry is optimized in the three-dimensional space without symmetry constraints. IR spectroscopy, ¹³C NMR, and XRD methods are used to determine the composition, structure, and geometry of the coordination site of the zinc(II) complex with L-histidine.

Behavior of gold films supported on the surface of a silver foil is studied using X-ray photoelectron spectroscopy (XPS) when heated in a vacuum or in nitrogen dioxide (under pressure of 10⁻⁵ mbar) at 200 °C. The initial gold film is 2–2.7 nm thick. It is shown that the gold film dissolves in the silver foil volume during the heating to form an Ag–Au alloy. The behavior of the ratio of the AgMVV Auger line intensity to the Ag3d photoemission line intensity testifies that the alloy surface is enriched with silver. The enrichment proceeds more efficiently when the system is heated in the presence of NO₂.

The crystal structure of [CuEn₃]WO₄ (En is ethylenediamine) is studied in the temperature range 100–390 K. Crystallographic data at 100 K are: a = 27.6903(8) Å, c = 9.9405(3) Å, space group P3̄, V = 6600.8(4) ų, Z = 18. Copper atomic coordination is a distorted square bipyramid. Four short Cu–N distances are within 2.038(5)–2.110(6) Å; two long distances are within 2.374(8)–2.514(7) Å. The lengths of N–H…O interionic contacts lie within 1.96–2.17 Å. A temperature elevation makes the Cu–N distances equal: at 298 K they are within 2.066(2)–2.256(3) Å(a = 16.0391(8) Å, c = 9.9608(6) Å, space group P3̄c1, V = 2219.1(3) ų, Z = 6), and at 390 K they are 2.151(6) Å(a = 9.2986(10) Å, c = 10.0520(14) Å, P3̄1c, V = 752.7(2) ų, Z = 2). In the range from 100 K to 390 K the average W–O distances decrease from 1.776 Å to 1.734 Å. Hirshfeld surfaces of complex cations are analyzed. It is shown that with increasing temperature the number of interionic N–H…O contacts decreases. The [CuEn₃]WO₄ phase is found to be unstable and on storing in air it transforms into [CuEn₂](WO₄)·2H₂O.

In order to obtain novel biologically active substances with various types of activity, hybrid compounds based on 2-(diphenylphosphoryl)acetohydrazide, isatin, and sterically hindered phenols are synthesized. Their molecular and crystal structures are determined by X-ray crystallography.

The complexes of 4-(2,4,6-trichlorophenyl)-3-thiosemicarbazide (HL¹) with transition metal cations VO(II), Co(II), Ni(II), Cu(II), Pd(II), and Pt(II) are prepared and characterized using elemental and thermal analyses, UV-visible spectrophotometry, FTIR, mass, and NMR spectroscopy, X-ray diffraction, and molar conductance and magnetic susceptibility measurements. The results show that the prepared chelates have the following chemical formulae and structures: [(VO)₂(L¹)(SO₄)(C₂H₅O)·H₂O] (square based pyramidal structure), [Co₂(HL¹)Cl₃C₂H₅OH]·Cl (square planar structure), [Ni(HL¹)Cl₂]·3H₂O (square planar structure), [Cu(L¹)₂(H₂O)₂] (octahedral structure), [Pd(HL¹)Cl₂]·H₂O (weakly distorted square planar structure), and [Pt(HL¹)Cl₂]·1/2H₂O (square planar structure). Generally, the complexes exhibit a high thermal stability, however, the Pd(II) and Pt(II) complexes are more stable than the other complexes. The ligand (HL¹), and its complexes are screened for their biological activity. Some of the complexes are found more biologically active than the parent ligand.

The copper-based polymer is synthesized using a slow evaporation method with an α-diimine chelator (1,10-phenanthroline) as the primary ligand. The synthesized polymer is characterized by various spectroscopic studies (FT-IR, UV-visible, EPR, luminescent), powder XRD and TGA techniques. Single crystal XRD studies reveal the molecular structure as a one-dimensional (1D) coordination polymer (CP) with the composition [Cu(phen)(NO₃)₂]_n. The FT-IR spectrum of CP further ascertains the binding modes of the ligand moiety. The copper ion is present in the +2 oxidation state and the geometry around the central metal ion is distorted square pyramidal. Moreover, CP shows a brilliant catecholase-like activity in methanol, which can easily oxidize the substrate 3,5-di-tert-butylcatechol (3,5-DTBC) to its respective quinone. Kinetic measurements suggest that the catechol oxidation rate follows saturation kinetics with respect to the substrate and first order kinetics with respect to the catalyst. CP shows a very good catalytic activity with K_cat = 8.28 h⁻¹.

In this work, two new In^III-based coordination polymers {(H₂NMe₂)₃[In(TATAB)₂](H₂O)₆}_n (1, H₃TATAB = 4,4′,4″-s-triazine-1,3,5-triyl-tri-p-aminobenzoic acid) and {(Me₂NH₂)₂[In₂(TTA)₂(FA)₂] (DMF)₃}_n (2, H₃TTA = 4,4′,4″-{[(2,4,6-trimethylbenzene-1,3,5-triyl)tris(methylene)]tris(oxy)}tribenzoic acid, HFA = 2-fluorobenzoic acid, DMF = N,N-dimethylformamide) are successfully prepared under solvothermal conditions and structurally characterized by the single crystal X-ray study (SCXRD) and the powder X-ray analysis (PXRD). In addition, the in vitro anticancer activity of compounds 1 and 2 on three human hemangioma cells (HMEC-1, EAhy926 and SV40) is further investigated.