Oxidation vs. coordination chemistry of the {MoV2O4}2+ species: A structural study

•Structures of novel polyoxomolybdates.•{MoV2O4}2+ unit forms complexes, gets partially or fully oxidized.•[MoV2O4(quin)3]–: a novel {MoV2O4}2+ complex with quinaldinate.•A hexadecanuclear cluster, [MoV4MoVI12O50]8–: product of a partial Mo(V) oxidation.•(PipeH)8[MoVI7O24][MoVIO4]·CH3CN: a fully-oxidized compound. The reaction systems consisting of mononuclear [MoVOCl4(H2O)]–, carboxylate-based ligand and acetonitrile have afforded three novel polyoxomolybdate compounds. All three were characterized by X-ray structure analysis on single-crystal. The combination with phthalic acid has produced (Et3NH)8[MoV4MoVI12O50]·2Py (MoV,VI16, Et3NH+ = a protonated triethylamine, Py = pyridine), a compound with the mixed-valence hexadecanuclear cluster anion. Its four pentavalent sites form part of well-known {MoV2O4}2+ units, the remaining twelve metal ions are fully-oxidized. The quinaldinate system has led to a genuine {MoV2O4}2+ complex with the carboxylate ligand, (Et3NH)[MoV2O4(quin)3]·CH3OH (MoV2, quin– = a deprotonated form of quinoline-2-carboxylic acid), and to a fully-oxidized compound, (PipeH)8[MoVI7O24][MoVIO4]·CH3CN (MoVI7MoVI, PipeH+ = a protonated piperidine). The latter compound contains a very rare combination of two oxomolybdate(VI) species, heptamolybdate [MoVI7O24]6– and monomolybdate [MoVIO4]2–. [Display omitted]