High-frequency (245 GHz) and X-band EPR study of stable dicopper radical complexes

摘要

Stable, readily accessible and in part even structurally established paramagnetic complex cations [Cu_2(μ-#eta#~4-BL)L_2]~+, BL = bridging ligand, L = Ph_2P(CH_2)_n PPh_2 or 2 PPh_3, were studied by high-frequency (245 GHz) and X-band EPR spectroscopy. The dicopper(I)/anion radical ligand formulation as opposed to a mixed-valent dimetal description is supported by the high-frequency EPR results which show g components between 2.0220 and 1.9968. The largest (rhombic) g anisotropy #DELTA#g was found for the system with BL=azodi-tert-butyl formate and L = Ph_2P(CH_2)_6PPh_2, and the smallest (axial)#DELTA#g splittings for 1,2,4,5-tetrazine-bridged species. There is a clear relation between #DELTA#g as obtained from the high-field measurements and the ~(63.65)Cu hyperfine coupling as measured from solution spectra in the X band.