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Journal of Structural Chemistry

2016 year, number 5

Features of the Ion Mobility and Phase Transitions in Hexafluoro Complex Compounds of Tantalum(V), Niobium(V), and Titanium(IV) with a Tetramethyl Ammonium Cation

V.Ya. Kavun, A.B. Slobodyuk, N.A. Didenko, R.L. Davidovich
Institute of Chemistry, Far East Branch, Russian Academy of Sciences, Vladivostok, Russia
Keywords: гексафторокомплексы, ниобий(V), тантал(V), титан(IV), тетраметиламмоний, ионная подвижность, фазовые переходы, спектры ЯМР F, H , ДСК, hexafluoro complexes, niobium(V), tantalum(V), titanium(IV), tetramethyl ammonium, ion mobility, phase transitions, F , H NMR spectra , DSC


19F, 1H NMR and DSC methods are employed to study the ion mobility and phase transitions in hexafluoro complex compounds of tantalum(V), niobium(V), and titanium(IV) with a tetramethyl ammonium cation. It is found that the transformation of NMR spectra observed in the temperature range 77(130)-450 K is due to a change in the form of ion motions in the anionic and cationic sublattices of the compounds under study. The main forms of ion motions in the temperature range 170-450 K are isotropic reorientations of TaF6, NbF6, TiF6 octahedra and tetramethyl ammonium ions. Two endoeffects with the maxima at 232.5 K and 256.5 K for [N(CH3)4]TaF6 and at 235 K and 250 K for [N(CH3)4]NbF6, which are observed in the DSC curve in the range 170-400 K, correspond to phase transitions whose occurrence practically does not affect the parameters of NMR spectra in the temperature range 230-260 K. For the [N(CH3)4]2TiF6 compound an endoeffect is observed near 422 K, which corresponds to the phase transition from the rhombohedral modification to the cubic one.