Vol 60, No 8 (2019)

Structure, energy characteristics, and magnetic properties of o-benzoquinone iron complexes with tetradentate macrocyclic nitrogen containing bases (pyridinophane and tris(2-pyridylmethyl)amine) are studied with a DFT (UTPSSh/6-311++G(d,p)) quantum chemical method. Electron withdrawing substituents in the redox-active ligand stabilize its dianionic form but do not significantly affect the energy difference between the electromers. Strong ferromagnetic exchange interactions are predicted in the isomers of complexes containing a high-spin divalent iron ion and the semiquinone form of o-benzoquinone. According to the calculations, all studied compounds can undergo thermally induced spin crossover transitions.

The formation of Pd_xAg_1-x thin films from the gas phase on silver substrates is modeled by molecular dynamics. The effect of substrate temperature on the structure of coatings of various compositions (x = 0, 0.25, 0.5, 0.75, 1) is studied in the range from 300 K to 900 K. The films are shown to have an unevenly deformed fcc structure over the entire range of considered temperatures and compositions. The surface of the coating is not smooth; it contains holes and cavities with a characteristic height difference of several angstroms. No misfit dislocations are formed in the studied systems. Higher substrate temperatures during the deposition of the coating lead to the increased average adsorption energy in the formed layer (which is true for all elemental compositions of the films.) This is caused by the fact that diffusion rate is higher on hotter substrates, and the surface of the coating is therefore smoothed. It is notable that the change of adsorption energy as a function of the substrate temperature during film deposition is directly proportional to the palladium content in the film. A high accuracy (above 0.01 eV) procedure is proposed for the calculation of cohesive energy in the film. This characteristic is shown to be virtually independent on the substrate temperature during nanolayer deposition. This is a direct indication that the structure of the coating volume is not changed, regardless of its elemental composition, as the temperature of formation increases.

A Cu(II) complex of the N,N′-dipyridoxyl(1,2-diaminobenzene) [=H₂L] Schiff base is newly synthesized. The complex is characterized experimentally and theoretically. The density functional theory methods are employed to calculate the optimized geometry along with the natural bond orbital analysis and the vibrational frequency analysis of the complex. The computed IR frequencies are in agreement with the experimental one, confirming the validity of the proposed geometry for the complex. In the optimized geometry of the octahedral complex, dianionic L^2– acts as a tetradentate ligand. Two azomethine nitrogen atoms and two phenolate oxygen atoms of the L^2– ligand occupy four square positions of the complex. Also, two methanol ligands are perpendicular to the square plane. The large energy gap between the frontier orbitals demonstrates the stability of the complex. The properties of the Cu–N and Cu–O bonds are investigated by the Atoms In Molecules analysis, too.

In this work we are interested in the synthesis of a new solid solution type NaPb_3–xCd_xCa(PO₄)₃; (0 ≤ _x ≤ 1). The lacunar apatite series are synthesized by a solid-state reaction and studied by X-ray diffraction, infrared and Raman scattering spectroscopy, thermal gravimetric analysis, and differential scanning calorimetry. The crystal structure of these compounds was refined using the Rietveld method. These compounds crystallize in the hexagonal system (space group P6₃/_m) with a number of units per crystal lattice Z = 2. The structure is formed by [PO₄]³⁻ tetrahedra and Pb²⁺/Ca²⁺/Cd²⁺ ions, which constitute the basic skeleton of the structure. The Pb²⁺/Ca²⁺/Cd²⁺ ions occupy the 6h sites, whereas the 4f sites are occupied in half by the Pb²⁺/Ca²⁺/Cd²⁺ ions and the other half by the Na⁺ ions. The observed frequencies in the Raman and infrared spectra are explained and discussed based on the factor group analysis and by comparison with similar apatites. The vibrational spectroscopy results are in good agreement with the X-ray diffraction measurements. The internal modes of (PO₄)³⁻ tetrahedra are assigned and corroborate well with the factor group analysis for the symmetry P6₃/m. We also investigated the thermal stability of these apatite materials by differential scanning calorimetry.

A heterotetranuclear zinc(II)-cerium(IV) complex [(ZnL)₂Ce(OAc)₂][Ce(NO₃)₆] · Py (H₂L = 6,6′-methoxy-2,2′-[1,2-ethylenedioxybis(nitrilomethylidyne)]diphenol and Py = pyridine) is successfully prepared by a one-pot reaction of a Salamo-type ligand H₂L with Zn(OAc)₂·2H₂O, Ce(NO₃)₃-6H₂O, and an auxiliary ligand Py. The Znⁿ-Ce^IV complex consists of one dicationic [(ZnL)₂Ce(OAc)₂]²⁺ unit with a deca-coordinated Ce^IV atom, one [Ce(NO₃)6]²⁻ dianionic unit with a dodeca-coordinated Ce^IV atom, and one uncoordinated Py molecule. Interestingly, the two Ce^IV atoms are positive tetravalent, which may probably be due to the oxidation of trivalent Ce^m atoms during the reaction. Moreover, the photophysical properties of the Znⁿ-Ce^IV complex are studied.

From a nitrate solution of platinum(IV) hydroxide, (C₄N₂H₁₂)[Pt(N03)6] salt containing a piperazinium cation is isolated. The salt structure is determined by X-ray crystallography. Crystallographic data are: a=15.589(1)Å, b= 12.919(1) Å, c = 9.889(9)Å, β = 08.625(4)°, space group C2/c, Z=4, ρ_calc⁼ 2.306 g/cm³. In the structure, [Pt(NO₃)₆]²⁻ anions having a shape of a trigonal antiprism are organized into a 3D network by the formation of hydrogen bonds with organic cations. For a series of salts containing [Pt(NO₃)₆]²⁻ and [Pt₂(ώ-OH)₂(NO₃)₈]²⁻ anionic platinum nitrato complexes a relationship between the structure and ¹⁹⁵Pt MAS NMR spectra is shown.

The isoxazole derivative 4-(3,5-dimethylisoxazol-4-yl)benzene-1,2-diol is synthesized and characterized by spectroscopy. The structure is further determined by single crystal X-ray diffraction. We also use the B3LYP method to calculate the optimized structure of the molecule by DFT using the 6-311+G(2d,p) basis set. A comparison of the obtained structures is made. The results show that the crystal structures determined by single crystal X-ray diffraction and the DFT calculation are very close.

Thin-film structures based on magnesium and ruthenium oxides are obtained by metal-organic chemical vapor deposition (MOCVD) on flat silicon substrates from volatile bis-(dipivaloylmethanato)(N, N, N’,N’-tetramethylethylenediamine)magnesium(II) and tris-(acetylacetonato)ruthenium(III) complexes in the presence of oxygen. The samples are studied by SEM, EDS, powder XRD, and differential dissolution; their emission characteristics are also measured. The features of the phase formation and the microstructure in the films formed are shown and different forms of magnesium and ruthenium oxides, including nonstoichiometric ones, are found. The MOCVD experimental parameters to form composite structures with high coefficients of electron-induced secondary electron emission (up to 7.2) are determined. These materials can be used as efficient emitting coatings in modern 3D electron multipliers.