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)

Abstract
Reaction of VO(acac)2 with 2-mercaptophenol (mpH2) in the presence of triethylamine gives the mononuclear tris complex (Et3NH)2[V(mp)3] (1), in which the vanadyl oxygen has been displaced. An analogous reaction using 2-mercapto-4-methylphenol (mmpH2) afforded (Et3NH)(PNP)[V(mmp)3] (2), which was structurally characterized. 2 crystallizes in the orthorhombic space group Pna21 with unit cell parameters (at −163 °C) a = 23.974(7) Å, b = 9.569(4) Å, c = 25.101(6) Å, 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(Ph4P)[VO(mp)2]·Et2O (3), which crystallizes in the triclinic space group P1̄ with unit cell parameters (at −135 °C) a = 12.185(4) Å, b = 12.658(4) Å, c = 14.244(4) Å, α = 103.19(2)°, β = 100.84(2)°, and γ = 114.17(2)°. 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 PPh4+ ions. The coordination geometry around the vanadium is square pyramidal, with a VO bond length of 1.611(5) Å. 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 I2, Cp2Fe+, or O2 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.

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