Single-crystal EPR study and DFT structure of the [Mo(CO)5PPh3]+· radical cation

Abstract A radical species characterized by a large g-anisotropy and a clearly resolved hyperfine structure with 95/97 Mo and 31 P nuclei is formed, at 77 K, by radiolysis of a single crystal of Mo(CO) 5 PPh 3 . The corresponding EPR signals disappear irreversibly with increasing temperature and the angular dependence of the various coupling constants imply a spin delocalization of ∼60% and ∼4% on the molybdenum and the phosphorus atoms, respectively and are, a priori , consistent with the trapping of a one-electron deficient centre. The ability of DFT to predict the EPR tensors for a 17-electron Mo (I) species is verified by calculating the g -tensor and the various 14 N and 13 C coupling tensors previously reported by Hayes for [Mo(CN) 5 NO] 3− . Calculations at the B3LYP/ZORA/SOMF level of theory show that, in contrast to Mo(CO) 5 PH 3 , one-electron oxidation of Mo(CO) 5 PPh 3 causes an appreciable change in the geometry of the complex. The g -tensor and the 95/97 Mo and 31 P isotropic and anisotropic coupling constants calculated for [Mo(CO) 5 PPh 3 ] +· confirm the trapping of this species in the irradiated crystal of Mo(CO) 5 PPh 3 ; they also show that the conformational modifications induced by the electron release are probably hindered by the nearby complexes.