Vanadium(V) complexes of mandelic acid

New vanadium complexes of mandelic acid (NMe4)(4)[V2O4((R)-mand)(2)][V2O4((S)-mand)(2)] (1), (NMe4)(2)-[V2O4((S)-mand)(2)]center dot H2O (2), (NEt4)(2)[V2O4((S)-mand)(2)]center dot H2O (3), (PPh4)(2)[V2O4((R)-mand)((S)-mand)]center dot 2H(3)CCOCH(3)center dot 2H(2)O (4), and (NH4)(2.5)(NEt4)(0.5)[V3O7((R)-mand)((S)-mand)]center dot 2H(2)O (5) (mand(2-) = mandelato ligand) have been synthesized and characterized by single crystal X-ray diffraction and FT-IR spectroscopy. The band assignment in the IR spectra was corroborated by DFT calculations. While the structures of 1-4 comprise the expected dinuclear [V2O4(mand)(2)](2-) (V2L2) anions, the structure of [V3O7((R)-mand)((S)-mand)](3-) (V3L2) in 5 is unique and represents a new structural type in vanadium(V) chemistry. Solution studies of vanadate with mandelic acid by V-51 NMR revealed the presence of two dominant species V2L2 and V3L2 in aqueous solutions and increasing fraction of V3L2 species at slightly acidic pH (pH approximate to 6).