title: Nonoxovanadium(IV) and oxovanadium(V) complexes with mixed O, X, O-donor ligands (X = S, Se, P, or PO).
abstract: Ligating properties of four potentially tridentate bisphenol ligands containing [O, X, O] donor atoms (X = S 1, Se 2, P 3, or P=O 4) toward the vanadium ions in +IV or +V oxidation states have been studied. Each ligand with different heterodonor atoms yields as expected nonoxovanadium(IV) complexes, V(IV)L(2), whose structures have been determined by X-ray diffraction methods as having six-coordinate V(IV), VO(4)X(2), core. Compounds 1-4 have also been studied with electrochemical methods, variable-temperature (2-295 K) magnetic susceptibility measurements, X-band electron paramagnetic resonance (EPR) (2-60 K) spectroscopy, and magnetic circular dichroism (MCD) (5 K) measurements. Electrochemical results suggest metal-centered oxidations to V(V) (i.e., no formation of phenoxyl radicals from the coordinated phenolates). A combination of density functional theory calculations and experimental EPR investigations indicates a dramatic effect of the heteroatoms on the electronic structure of 1-4 with consequent reordering of the energy levels; 1 and 3 possess a trigonal ground state (d(z)()(2))(1), but 4 with the phosphoryl oxygen as the heterodonor atom in contrast exhibits a tetragonal ground state, (d(xy)())(1). On the basis of the intense electronic transitions in absorption spectra, all electronic transitions observed for 4 have been assigned to ligand-to-metal charge-transfer transitions, which have been confirmed by preliminary resonance Raman measurements and C/D ratios obtained from low-temperature MCD spectroscopy. Moreover, diamagnetic complexes 5 and 6 containing mononuclear and dinuclear oxovanadium(V) units have also been synthesized and structurally and spectroscopically ((51)V NMR) characterized.
authors.affiliation: Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany.
authors.forename: Tapan K
authors.initials: TK
authors.lastname: Paine
authors.forename: Thomas
authors.initials: T
authors.lastname: Weyhermüller
authors.forename: Leonardo D
authors.initials: LD
authors.lastname: Slep
authors.forename: Frank
authors.initials: F
authors.lastname: Neese
authors.forename: Eckhard
authors.initials: E
authors.lastname: Bill
authors.forename: Eberhard
authors.initials: E
authors.lastname: Bothe
authors.forename: Karl
authors.initials: K
authors.lastname: Wieghardt
authors.forename: Phalguni
authors.initials: P
authors.lastname: Chaudhuri