Synthesis, structural characterization and spectroscopic studies of bis tetramethylammonium hexabromostannate [N(CH3)4]2SnBr6

Abstract The compound [TMA] 2 SnBr 6 (TMA = Tetramethylammonium = N(CH 3 ) 4 ) has been synthesized by slow evaporation and its crystal structure was determined by single crystal X-ray diffraction. The [TMA] 2 SnBr 6 crystallizes in the cubic system (Fm 3 ¯ m space group) with cell parameter a = 13.2554(15) A. It can be considered as derived from a perovskite structure in which half of the octahedral symmetry sites are occupied by [SnBr 6 ] 2- octahedra and half by vacancies. The purity of the compound was checked by EDS measurement and Rietveld refinements. The Raman and infrared spectra at room temperature are recorded in the wavenumber range 10–3600 cm −1 and 400-4000 cm −1 , respectively. Ab-initio calculations have been performed using the Gaussian 98 program at room temperature. Hartree-Fock (HF) and B3LYP density functional theory (DFT) methods with 6-31G (d) and LanL2DZ basis sets were used to obtain equilibrium geometry and the fundamental vibrational frequencies and spectroscopic intensities of the free polyhedra [(N(CH 3 ) 4 ] + and [SnBr 6 ] 2- . The overall results are consistent with the experimental ones and group theory analysis, but also clearly show extra features that suggest disorder of the methyl groups of TMA.