EPR and optical studies in pseudotetrahedral tetramethyl ammonium copper {II) bromide

EPR studies of single crystal copper tetramethyl ammonium bromide, T2CuBr4(T = (CH3~4N] in the temperature range 77-300 K indicate the largest covalency in this compound compared to similar halogenated pseudotetrahedral copper compounds. The angle cos _,r between the c axis and the ionic g 11 axis is 12' and 65' at 250 and 220 K, respectively. The change is continuous down to 200 K. The g shift between 300 and 200 K indicates an increase in the strength of the ligand field with lowering of temperature. The magnetic susceptibility ellipsoid and the g -tensor ellipsoid do not coincide in this material. Optical spectra in T2(Cu:Zn)Br4 have been assigned. The nonobservation of an EPR signal in T,(Cu:Zn)Br4 and Cs2CuBr4 indicates that ligand field properties in these pseudotetrahedral compounds are quite different from that of T2CuBr4