Electron spin resonance and relaxation of tetrahedrally coordinated copper(11) in some complex halides

Electron spin resonance and relaxation measurements are reported for some copper salts in which the Cu 2+ ion has tetrahedral coordination. For the CuCl 4 2− ion in Cs 2 CuCl 4 , the results are in some respects at variance with those previously reported [1]. The crystallographic cell parameters for [(C 4 H 9 ) 4 N] 2 CuBr 4 have been measured, and in this material a single broad asymmetric ESR line is reported, about 145 G wide at X‐band, having principal g ‐values of 2.068, 2.053, and 2.220. Spin‐lattice relaxation times measured by both pulse and continuous saturation methods yielded values of T 1 in the range 60 μs at 4.2 K to 140 μs at 1.7 K. These are compared with the much larger values predicted for copper in other tetrahedrally coordinated materials [2]. The ESR spectra of CuCl 4 2− and CuBr 4 2− ion adsorbed on an ion exchange resin are compared with those from powdered samples of the above two complexes. Measurements of T 1 for the CuBr 4 2− ion on the resin yielded values of 100 μs at 4.2 K and 280 μs at 1.86 K. It is concluded that the complex halides are not a suitable system in which to study relaxation behaviour of Cu 2+ in a tetrahedral crystal field.