title: Nonoxido V(IV) Complexes: Prediction of the EPR Spectrum and Electronic Structure of Simple Coordination Compounds and Amavadin.
abstract: Density functional theory (DFT) calculations of the (51)V 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 Aiso and Ai (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 Aiso or Ai is the double hybrid B2PLYP. With this functional and the basis set VTZ, it is possible to predict the Aiso and Az 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 Ax, Ay, and Az. For "type 1" spectra, Az ≫ Ax ≈ Ay and Az is in the range of (135-155) × 10(-4) cm(-1); for "type 2" spectra, Ax ≈ Ay ≫ Az and Ax ≈ Ay are in the range of (90-120) × 10(-4) cm(-1); and for the intermediate spectra of "type 3", Az > Ay > Ax or Ax > Ay > Az, with Az or Ax values in the range of (120-135) × 10(-4) cm(-1). The electronic structure of the V(IV) species was also discussed, and the results showed that the values of Ax or Az are correlated with the percent contribution of V-dxy orbital in the SOMO. Similarly to V(IV)O species, for amavadin the SOMO is based mainly on the V-dxy orbital, and this accounts for the large experimental value of Az (153 × 10(-4) cm(-1)).
authors.affiliation: Istituto di Chimica Biomolecolare, Consiglio Nazionale delle Ricerche, UOS di Sassari, Trav. La Crucca 3, I-07040 Sassari, Italy.
authors.forename: Daniele
authors.initials: D
authors.lastname: Sanna
authors.affiliation: Dipartimento di Chimica e Farmacia, Università di Sassari , Via Vienna 2, I-07100 Sassari, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Sciortino
authors.affiliation: Dipartimento di Chimica e Farmacia, Università di Sassari , Via Vienna 2, I-07100 Sassari, Italy.
authors.forename: Valeria
authors.initials: V
authors.lastname: Ugone
authors.affiliation: Dipartimento di Chimica e Farmacia, Università di Sassari , Via Vienna 2, I-07100 Sassari, Italy.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Micera
authors.affiliation: Dipartimento di Chimica e Farmacia, Università di Sassari , Via Vienna 2, I-07100 Sassari, Italy.
authors.forename: Eugenio
authors.initials: E
authors.lastname: Garribba
mesh_terms: D000409:Alanine / Q000031:analogs & derivatives* / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D006877:Hydroxamic Acids / Q000737:chemistry*; D008958:Models, Molecular; D017968:Vanadium Compounds / Q000737:chemistry*
chemical_list: D006877:Hydroxamic Acids; C502921:N-hydroxyimino-2,2'-dipropionic acid; D017968:Vanadium Compounds; D000409:Alanine