EPR Measurements corroborate information concerning the nature of (H2O)5Crm-aIkyI complexes

The X-band EPR spectra of [(H2O)5Crln-CHCl2]2+, [(H2O)5CrIII-CHCBrJ2+, [(H2O)5Crm-CH3]2+, [(H2O)5Crw-CH2CO2H]2+ and [(H2O)JCrIII-CH(CH3)OC2H5]2+ were measured at liquid helium temperatures. For all complexes the major derivative signal is observed at £'perp - 4 with weaker signals at g'par = 2 and g' »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"' and EID = 0.06, respectively. Based on these results the (H2O)5Cr-R2+ complexes studied here are best described as chromium(m) 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.