Nonoxido VIV Complexes: Prediction of the EPR Spectrum and Electronic Structure of Simple Coordination Compounds and Amavadin

Density functional theory (DFT) calculations of the V-51 hyperfine coupling (HFC) tensor A have been completed for 20 bare V-IV complexes with different donor sets, electric charges, and coordination geometries. Calculations were performed with ORCA and Gaussian software, using functionals BP86, TPSS0, B1LYP, PBE0, B3LYP, B3P, B3PW, O3LYP, BHandHLYP, BHandH, and B2PLYP. Among the basis sets, 6-311g(d,p), 6-311++g(d,p), VTZ,-cc-pVTZ, def2-TZVPP, and the core properties CP(PPP) were tested. The experimental A(ISO) and A(i) (where i = x or z, depending On the geometry and electronic structure of V-IV complex) were compared with the values calculated by DFT methods. The results indicated that, based on the mean absolute percentage deviation (MAPD), the best functional to predict A(iso) or A(i) is the double hybrid B2PLYP. With this functional and the basis set VTZ, it is possible to predict the A(iso) and A(z) of the EPR spectrum of amavadin with deviations of -1.1% and -2.0% from the experimental values. The results allowed us to divide the spectra of nonoxido V-IV compounds in three types-called type 1, type 2, and type 3, characterized by different composition of the singly occupied molecular orbital (SOMO) and relationship between the values of A(x), A(y), and A(z). For type 1 spectra, A(z) >> A(x) approximate to A(y) and A(z) is in the range of (135-155) x 10(-4) cm(-1); for type 2 spectra, A(x) approximate to A(y) >> A(z) and A(x) approximate to A(y) are in the range of (90-120) x 10(-4) cm(-1); and for the intermediate spectra of type 3, A(z) > A(y) > A(x) or A(x) > A(y), > A(z,) with A(z) or A(x) values in the range of (120-135) x 10(-4) cm(-1). The electronic structure of the V-IV species was also discussed, and the results showed that the values of A(x) or A(z) are correlated with the percent contribution of V-d(xy) orbital in the SOMO. Similarly to (VO)-O-IV species, for amavadin the SOMO is based mainly on the V-d(xy), orbital, and this accounts for the large experimental value of A(z) (153 X 10(-4) cm(-1)).