Structural characteristics for phase transitions of [N(CH3)4]2CuCl4 by 13C CP/MAS NMR and 14N NMR

Abstract

Structure geometry changes in [N(CH3)4]2CuCl4 near the phase transition temperature were studied by 13C CP/MAS NMR and 14N NMR spectrum. We distinguished the two chemically inequivalent N(1)(CH3)4 and N(2)(CH3)4 groups by 13C CP/MAS NMR and 14N NMR spectrum. The abrupt changes in chemical shifts and the split of the NMR signals near the phase transition temperatures for 13C and 14N are explained by a structural phase transition, implying that the structural geometry depends on the temperature. The mechanism behind this phase transition is based on ferroelasticity, and is also mainly related to the 14N ions in N(CH3)4 ions. Furthermore, both phases III and IV exhibit ferroelastic properties with identical orientational domains.