Q-band single-crystal EPR study and molecular orbital calculations of [(C6H5)(4)As][Re(VI)NCl4/Re(V)OCl4]

A Q-band single-crystal EPR study of tetraphenylarsoniumtetrachloro-nitrido rhenate(VI), [(C6H5)(4)As][Re-VI NCl4], diamagnetically diluted by the isoe lectronic oxorhenate(V) complex is reported. The EPR spectra are typical of an ion with 5d(1) (S = 1/2) configuration and are influenced by large rhen ium hyperfine coupling constants and nuclear quadrupole interactions. They are characterized by well-resolved Re-185.187 hyperfine patterns with almos t equal spacings and the occurrence of "forbidden" transitions (Delta m(1) = +/-1, Delta m(1) = +/-2). The Re-185.187 hyperfine parameters as well as the data obtained from densi ty functional theory (DFT) and the extended Huckel theory (EHT) molecular o rbital calculations are used to analyze the spin density distribution in th e system under study. Thereby, the negative sign found for the spin density at the nitrogen from DFT is mainly determined by spin polarization. In add ition, both MO methods are used to calculate the electric field gradient be ing responsible for the Re-185.187 nuclear quadrupole coupling. (C) 2000 El sevier Science B.V. All rights reserved.