EPR Measurements corroborate information concerning the nature of (H2O)5CrIII–alkyl complexes

Abstract

The X-band EPR spectra of [(H₂O)₅Cr^III–CHCl₂]²⁺, [(H₂O)₅Cr^III–CHCBr₂]²⁺, [(H₂O)₅Cr^III–CH₃]²⁺, [(H₂O)₅Cr^III–CH₂CO₂H]²⁺ and [(H₂O)₅Cr^III–CH(CH₃)OC₂H₅]²⁺ were measured at liquid helium temperatures. For all complexes the major derivative signal is observed at g′_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⁻¹ and E/D = 0.06, respectively. Based on these results the (H₂O)₅Cr–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 larger covalent nature than the Cr–X bond, where X = halide, etc.