Vanadium(IV) complexes with mixed O,S donor ligands. Syntheses, structures, and properties of the anions tris(2-mercapto-4-methylphenolato)vanadate(IV) and bis(2-mercaptophenolato) oxovanadate(IV)

Reaction of VO(acac)(2) with 2-mercaptophenol (mpH(2)) in the presence of triethylamine gives the mononuclear tris complex (Et(3)NH)(2)[V(mp)(3)] (1), in which the vanadyl oxygen has been displaced. An analogous reaction using 2-mercapto-4-methylphenol (mmpH(2)) afforded (Et(3)NH)(PNP)[V(mmp)(3)] (2), which was structurally characterized. 2 crystallizes in the orthorhombic space group Pna2(1) with unit cell parameters (at -163 degrees C) a = 23.974(7) Angstrom, b = 9.569(4) Angstrom, c = 25.101(6) Angstrom, and Z = 4. The coordination geometry around the vanadium is between octahedral and trigonal prismatic. Reaction of VO(acac)(2) with the sodium salt of 2-mercaptophenol produces the vanadyl(IV) complex Na(Ph(4)P)[VO(mp)(2)]. Et(2)O (3), which crystallizes in the triclinic space group <P(1)over bar > with unit cell parameters (at -135 degrees C) a = 12.185(4) Angstrom, b = 12.658(4) Angstrom, c = 14.244(4) Angstrom, alpha = 103.19(2)degrees, beta = 100.84(2)degrees, and gamma = 114.17(2)degrees. The unit cell of 3 contains a pair of symmetry-related [VO(mp)(2)](2-) units bridged through vanadyl and ligand oxygen atoms by a pair of sodium ions, in addition to two PPh(4)(+) ions. The coordination geometry around the vanadium is square pyramidal, with a V=O bond length of 1.611(5) Angstrom. 1, 2, and 3 are characterized by IR and UV-vis spectroscopies, magnetic susceptibility, EPR spectroscopy, and cyclic voltammetry. 1 and 2 can be oxidized by I-2, Cp(2)Fe(+), or O-2 to [V(mp)(3)](-) and [V(mmp)(3)](-), respectively, which in turn can be reduced back to the dianions by oxalate ion. These reversible redox processes can be followed by UV-vis spectroscopy.