6533b7ddfe1ef96bd127522b

RESEARCH PRODUCT

Structure and properties of tris(tetramethylammonium) nonabromodiarsenate(III), [(CH3)4N]3[As2Br9]

subject

description

The new tetramethylammonium bromoarsenate(III) crystal [(CH3)4N]3 [As2Br9] has been synthesized and its phase behaviour established by differential scanning calorimetry and dilatometry. Three phase transitions are found: at 346/346 K , at 165/171 K and at 157/165 K on cooling/heating. Single-crystal x-ray diffraction studies of phases I (at 370 K) and II (at 298 K) have shown that the structure comprises discrete [As2Br9]3− anions and disordered [(CH3)4N]+ cations. Phase II crystallizes in the polar space group P31c; its polar nature was confirmed by pyroelectric measurements. Phase I has higher symmetry, P63mc or . Dielectric dispersion measurements revealed a relaxation process in the crystal. The ferroic (ferroelastic) properties were found below 165 K (the transition). The NMR studies indicate the subtle change in the motional state of the tetramethylammonium cations through all observed phase transitions.