Polynuclear molybdenum and tungsten complexes of 3-hydroxypicolinic acid and the crystal structures of (nBu4N)2[Mo4O12(picOH)2] and (nHex4N)2[Mo2O6(picOH)2]

New polynuclear molybdenum(VI) and tungsten(VI) complexes with 3-hydroxypicolinic acid (HpicOH) (nBu4N)2[Mo4O12(picOH)2] 1, (nHex4N)2[Mo2O6(picOH)2] 2, (BezPh3P)2[W2O6(picOH)2] 3 (Bez = benzyl) and [M2O5(picOH)2]·nH2O (M = Mo(VI), n = 2 4 or W(VI), n = 8 5) have been prepared. The crystal structures of 1 and 2 were determined by X-ray diffraction. The tetramolybdate 1 containing two coordinatively bound 3-hydroxypicolinate anions is a rare example of a discrete tetranuclear molybdenum-oxo cluster showing a Mo4O12 core with the molybdenum centres bonded through oxo bridges only; the organic ligands being in a peripheral position. Infrared, 1H and 13C-{1H} NMR spectroscopic data for the complexes are presented together with electrochemical characterization by cyclic voltammetry. These complexes are active toward oxygen atom transfer reactions and can catalyze the oxidation of benzoin (1,2-diphenyl-2-hydroxyethanone) with dmso.