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

• Structures of novel polyoxomolybdates. • {Mo V 2 O 4 } 2+ unit forms complexes, gets partially or fully oxidized. • [Mo V 2 O 4 (quin) 3 ] – : a novel {Mo V 2 O 4 } 2+ complex with quinaldinate. • A hexadecanuclear cluster, [Mo V 4 Mo VI 12 O 50 ] 8– : product of a partial Mo(V) oxidation. • (PipeH) 8 [Mo VI 7 O 24 ][Mo VI O 4 ]·CH 3 CN: a fully-oxidized compound. The reaction systems consisting of mononuclear [Mo V OCl 4 (H 2 O)] – , 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 (Et 3 NH) 8 [Mo V 4 Mo VI 12 O 50 ]·2Py ( Mo V,VI 16 , Et 3 NH + = a protonated triethylamine, Py = pyridine), a compound with the mixed-valence hexadecanuclear cluster anion. Its four pentavalent sites form part of well-known {Mo V 2 O 4 } 2+ units, the remaining twelve metal ions are fully-oxidized. The quinaldinate system has led to a genuine {Mo V 2 O 4 } 2+ complex with the carboxylate ligand, (Et 3 NH)[Mo V 2 O 4 (quin) 3 ]·CH 3 OH ( Mo V 2 , quin – = a deprotonated form of quinoline-2-carboxylic acid), and to a fully-oxidized compound, (PipeH) 8 [Mo VI 7 O 24 ][Mo VI O 4 ]·CH 3 CN ( Mo VI 7 Mo VI , PipeH + = a protonated piperidine). The latter compound contains a very rare combination of two oxomolybdate(VI) species, heptamolybdate [Mo VI 7 O 24 ] 6– and monomolybdate [Mo VI O 4 ] 2– .