Q-Band single-crystal EPR study and molecular orbital calculations of [C₆H₅)₄As][ReVINCl₄/ReVOCl₄]

A Q-band single-crystal EPR study of tetraphenylarsoniumtetrachloro-nitridorhenate(VI), [(C6H5)4As][ReVINCl4], diamagnetically diluted by the isoelectronic oxorhenate(V) complex is reported. The EPR spectra are typical of an ion with 5d1 (S = 1/2) configuration and are influenced by large rhenium hyperfine coupling constants and nuclear quadrupole interactions. They are characterized by well-resolved 185,187Re hyperfine patterns with almost equal spacings and the occurrence of "forbidden" transitions (DmI = ± 1, DmI = ± 2).
The 185,187Re hyperfine parameters as well as the data obtained from density functional theory (DFT) and extended Hückel theory (EHT) molecular orbital calculations are used to analyze the spin-density distribution in the system under study. Thereby, the negative sign found for the spin-density at the nitrogen from DFT is mainly determined by spin polarization. In addition, both MO methods are used to calculate the electric field gradient being responsible for the 185,187Re nuclear quadrupole coupling.