Novel hydrogenmaleato molybdenum(V) complexes based on a dinuclear metal–metal bonded unit: syntheses and structural characterization of (PyH)3[Mo2O4Cl4(OOCCHCHCOOH)] and (PyH)3[Mo2O4Br4(OOCCHCHCOOH)] · CH3CN

Reactions of pyridinum hydrogenmaleate with mononuclear oxohalomolybdates produced (PyH)3[Mo2O4X4(OOCCHCHCOOH)] (X=Cl, Br), the first molybdenum(V) complexes with hydrogenmaleato ligand. The X-ray structure analysis revealed in both the {Mo2O4}2+ core with hydrogenmaleate in a μ2-bis(monodentate) binding mode forming a third bridge between a pair of molybdenum atoms linked by a single metal–metal bond. A pair of halo ligands completes a distorted octahedral environment of each metal in the {Mo2O4}2+ unit.