Structures and phase transitions of (BrCH2CH2NH3)(2)CdBr4 and (BrCH2CH2CH2NH3)(2)CdBr4 as investigated by Br-81 NQR, DTA, and single-crystal X-ray diffraction

摘要

The crystal structures of (BrCH2CH2NH3)(2)CdBr4 (1) and (BrCH2CH2CH2NH3)(2)CdBr4 (2) have been determined at T = 113 K: orthorhombic, Pbcn, a = 843.8(4), b = 775.4(4), c = 2339.6(11) pm, Z = 4 for 1; orthorhombic, Pbcn, a = 858.7(3), b = 783.6(2), c = 2519.4(7) pm, Z = 4 for 2. Both crystals are isomorphic, showing distinctive layered perovskite-related structures, in which the cations orient their aliphatic parts toward each other in their cation layers and connect to the infinite anion layers with their ammonium parts through N-H center dot center dot center dot Br hydrogen bonds. Br-81 NQR and differential thermal analysis measurements for both compounds revealed the existence of successive phase transitions as seen in n-(CH3CH2CH2NH3)(2)CdBr4 (3). These phase transitions appear to be induced by the activated motions of the cations. The changes in the hydrogen bonding schemes resulting from the motions of the cations lead to the different phases of the respective crystals.