Molecular dynamics of cations and anions by 1H MAS NMR, 13C CP/MAS NMR, 14N NMR, and 113Cd NMR in hybrid organic-inorganic (CH3NH3)2CdBr4

Abstract

The local structure of (CH3NH3)2CdBr4 as a function of temperature was investigated by 1H MAS NMR, 13C CP/MAS NMR, 14N NMR, and 113Cd NMR, with emphasis on the role of the CH3NH3+ cation and CdBr42− anion. The chemically and physically inequivalent CH3NH3+ groups, CH3(1) and CH3(2), NH3(1) and NH3(2), were clearly distinguished by 13C CP/MAS NMR and 14N NMR spectra. In addition, to obtain detailed information on the dynamics of the crystal, the spin-lattice relaxation times T1ρ of 1H and 13C and the spin-lattice relaxation time T1 of 113Cd were measured. The T1ρ of 13C showed a minimum and is governed by the tumbling motion of the CH3 groups, indicating that the 1H and 13C atoms in the CH3NH3+ groups exhibit high mobility at high temperatures. The spin-lattice relaxation time thus provides insight into the rates of cation reorientation at high temperatures.