Dynamic orientation disorder in rubidium fluorotantalate. Synchronous Ta–O and Ta–F vibrations

The oxygen-containing rubidium fluorotantalate Rb₂TaO_xF_7−2x (x = 0.3) was synthesized in a single crystal form and its RT and LT structures were determined by X-ray diffraction. The structures include dynamically disordered seven-coordinated tantalum anions in the form of capped trigonal prisms. The oxygen presence was revealed by the appearance of the infrared band in the range of 700–800 cm⁻¹ assigned to totally synchronous Ta–O and Ta–F vibrations as a result of the distances equalization due to fast reorientations of a seven-coordinated polyhedron. The phase transition at 145 K is accompanied by the syngony change from tetragonal to orthorhombic and appearance of the 920 cm⁻¹ vibration assigned to a common terminal tantalum–oxygen triple bond.     

Spectral-Luminescent Properties and Molecular Orbital Treatment of Some Mono- and Difluoroquinolones

Electronic absorption and luminescent spectra of nonfluorinated nalidixic (nlqH) and pipemidic acid (pifqH), monofluoroquinolones – norfloxacin (nfqH) and pefloxacin (pfqH) as well as of their difluorinated analogs 1-ethyl-6,8-difluoro-1,4-dihydro-7-(1-(4-methylpiperazinyl) – 4-oxo-3-quinolinecarboxylic (mdfqH) acid and 1-ethyl-6,8-difluoro-1,4-dihydro-7-(1-piperazinyl) – 4-oxo-3-quinolinecarboxylic acid (dfqH) - were investigated. Quantum yields, lifetimes of excited states and rate constants of radiative and nonradiative transitions of the compounds were measured. The Mulliken charges of atoms from these compounds were calculated by quantum-chemical complex GAMESS. Differences in the electronic structures of these compounds and their spectral-luminescent characteristics were compared with the data of the phototoxicity degree of fluoroquinolones. Analysis of the Mulliken charges of the difluoroquinolones points to the changes of the redistribution of the electron density along π-conjugated system, and on the oxygen atoms of the carbonyl and carboxyl groups. The analysis of the molecular orbitals involved in the electronic transitions of the compounds revealed that both defluorination and piperazine photolysis are photodecomposition mechanisms which may take place in the excited states of these compounds. The relationship between the location order of the π-π* excited levels of the FQs and the degree of their phototoxicity has been determined     

Polymorphism and Intramolecular Proton Transfer in Fluoroquinolone Compounds

Electronic absorption, luminescence, IR and Raman spectra of polymorphous forms of fluoroquinolones were investigated. Assignment of the band maxima due to π→π* and n→π* electronic transitions were done. The structural changes are responsible for the absorption band modifications. One-electron transitions in the long wavelength region, excitation wavelengths, oscillator strengths and involved molecular orbitals for the zwitter-ionic and cationic protonated forms for different fluoroquinolones were calculated with quantum-chemical and molecular dynamic methods. The electron density redistributions on the FQs separate fragments during the photoexcitation to the S₁*-state were carry out by Mulliken calculations. It was shown that the degree of neutral and zwitter-ion FQs penetration through the bacterium membrane is different.     

Synthesis,structure, physicochemical properties,and solid-phase thermolysis of Co<Subscript>2</Subscript>Sm(Piv)<Subscript>7</Subscript>(2,4-Lut)<Subscript>2</Subscript>

Heterometallic pivalate Co₂Sm(Piv)₇(2,4-Lut)₂ (1) was prepared for the first time and structurally characterized at 293 and 160 K. Antiferromagnetic exchange interactions are dominant in complex 1. This compound experiences a first-order phase transition within 210–260 K. A set of thermodynamic functions was obtained for this complex (C _p , H _T ⁰ - H ₁₈₀ ⁰ , and S _T ⁰ ), and parameters were determined for solid-phase thermolysis where samarium cobaltate SmCoO₃ is the only product.     

Yttrium complexation with benzoic acid and tris(hydroxymethyl)aminomethane

Yttrium complexation in extraction systems with benzoic acid (BA) and tris(hydroxymethyl)aminomethane (THMAM) was studied. The growth of yttrium distribution ratios in this system is caused by the formation of different-ligand coordination compounds of yttrium with BA and THMAM. Quantum chemical calculations for the formation energy of different-ligand complex showed that the most stable complex forms when yttrium atom coordinates to two THMAM molecules via oxygen and nitrogen atoms and to one THMAM molecule via nitrogen atom. The complex is stable in both bidentate and monodentate coordination of the carboxyl groups of benzoic acid to yttrium atom. Obtained yttrium extracts were used for the synthesis of complex-oxide nanosized cathodophosphors by extraction-pyrolytic technique.     

The role of water molecules in the interfragmental charge transfer of the protolytic forms of fluoroquinolones in the ground and excited states

Quantum-chemical analysis (TD-DFT/B3LYP/6-31G) of the influence of H-bonding in the donor-acceptor fluoroquinolone compounds with the water molecules on the interfragmentary charge transfer was carried out. The values of charge transfer between the molecular fragments in the transition from the ground into the singlet excited state were calculated. It was found that, depending on the protolytic form of a compound, the frontier molecular orbitals are localized on different fragments, which leads to the specificity of the formation of the electron density transfer channel. The influence of individual substituents in the quinolones on the localization of particular MOs is relatively insignificant.     

Thermal decomposition of dinuclear complexes LM(μ-OOCR)<Subscript>4</Subscript>ML (L is α-substituted pyridine)

The solid-state thermal decomposition of the tetrabridged dinuclear Mn^II, Fe^II, Co^II, Ni^II, and Cu^II pivalate complexes with apical α-substituted pyridine ligands containing different substituents (2,3-dimethylpyridine or quinoline) was studied by differential scanning calorimetry and thermogravimetry. The decomposition of the Co^II complexes is accompanied by the aggregation to form the volatile octanuclear complex Co₈(μ₄-O)₂(μ_n-OOCCMe₃)₁₂, where n = 2 or 3, whereas the thermolysis of the Mn^II, Fe^II, Ni^II, and Cu^II complexes is accompanied by the degradation of the starting compounds, the phase composition of the decomposition products being substantially dependent on the nature of metal and the apical organic ligand. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1650–1659, September, 2007.