EPR Measurements corroborate information concerning the nature of (H_2O)_5Cr~(III)-alkyl complexes

摘要

The X-band EPR spectra of [(H_2O)_5Cr~(III)-CHCl_2]~(2+), [(H_2O)_5Cr~(III)-CHCBr_2]~(2+), [(H_2O)_5Cr~(III)-CH_3]~(2+), [(H_2O)_5Cr~(III)-CH_2CO_2H]~(2+) and [(H_2O)_5Cr~(III)-CH(CH_3)OC_2H_5]~(2+) were measured at liquid helium temperatures. For all complexes the major derivative signal is observed at g'_(perp) approx= 4 with weaker signals at g'_(par) approx= 2 and g' approx= 5.9. The signals broaden with increasing temperature and can not be observed at T >= 20 K, the low-temperature spectra could readily be simulated by using the spin Hamiltonian formalism for S = 3/2 with axial and rhombic zero-field splitting parameters D = -1.6 cm~(-1)) and E/D = 0.06, respectively. Based on these results the (H_2O)_5Cr-R~(2+) complexes studied here are best described as chromium(III) compounds with a covalent chromium-carbon bond. In accord with expectations, this bond has a considerably larger covalent nature than the Cr-X bond, where X = halide, etc.