EPR measurements corroborate information concerning the nature of (H2O)(5)Cr-III-alkyl complexes

The X-band EPR spectra of [(H2O)(5)Cr-III-CHCl2](2+), [(H2O)(5)Cr-III-CHCBr 2](2+), [(H2O)(5)Cr-III-CH3](2+), [(H2O)(5)Cr-III-CH2CO2H](2+) and [(H2O)(5 )Cr-III-CH(CH3)OC2H5](2+) were measured at liquid helium temperatures. For all complexes the major derivative signal is observed at g'(perp)approximat e to 4 with weaker signals at g'(par)approximate to 2 and g'approximate to 5.9. The signals broaden with increasing temperature and can not be observe d at T greater than or equal to 20 K. the low-temperature spectra could rea dily be simulated by using the spin Hamiltonian formalism for S=3/2 with ax ial and rhombic zero-field splitting parameters D=-1.6 cm(-1) and E/D=0.06, respectively. Based on these results the (H2O)(5)Cr-R2+ 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 lar ger covalent nature than the Cr-X bond, where X=halide, etc.