PHASE-TRANSITIONS AND CATION DYNAMICS IN [(CH3)(2)NH2]3BI2CL9 (DMACB)- PROTON SPIN RELAXATION STUDIES

Tris(dimethylammonium nona chloro dibismuthate), [(CH3]2NH2]3Bi2Cl9, f amily has been investigated through proton magnetic resonance and rela xation measurements as a function of temperature. Results indicate the presence of two phase transitions at 152 and 78 K, accompanied by cha nges in the reorientational dynamics of the cation groups. Above 152 K , the [(CH3)(2)NH2](+) groups are undergoing isotropic reorientations with dynamic inequivalence, while in contrast they exhibit two-fold ro tations in the low temperature phase. The phase transition at 78 K see ms to be associated with considerable change in the orientational orde r of the molecular groups. Comparison is made with similar antimony (S b) substituted compounds to discuss the microscopic effects of substit ution of heavier bismuth (Bi) metal atom. Copyright (C) 1996 Published by Elsevier Science Ltd