Synthesis and properties of mononuclear and binuclear molybdenum complexes derived from bis(2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone

The monomer molybdenum(VI) complex [MoO2(napoxlhH2)]·2H2O (1) has been synthesized from the reaction of MoO2(acac)2 with bis(2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone (napoxlhH4) in 1:1 molar ratio in ethanol under reflux. This complex on reaction with pyridine/3-picoline/4-picoline yielded the dimer molybdenum(VI) complexes [Mo2O4(napoxlhH2)2(A)2]·2H2O (A = py (2), 3-pic (3), 4-pic (4)), whereas reaction with isonicotinoylhydrazine (inhH3) and salicyloylhydrazine (sylshH3) lead to the reduction of the metal centre yielding monomeric molybdenum(V) complexes [Mo(napoxlhH2)(hzid)]·2H2O (where hzidH3 = inhH3 (5) and sylshH3 (6)). The complexes have been characterized by elemental analyses, molecular weight determinations, molar conductance data, magnetic moment data, electronic, IR, ESR and 1H NMR spectroscopic studies. The complexes (5) and (6) are paramagnetic to the extent of one unpaired electron. The electronic spectra of the complexes are dominated by strong charge transfer bands. In all of the complexes, the principal dihydrazone ligand has been suggested to coordinate to the metal centres in the anti-cis-configuration. The complexes (1), (5) and (6) are suggested to have six-coordinate octahedral stereochemistry around molybdenum(VI) and molybdenum(V) metal centres, respectively, while the complexes (2)-(4) are suggested to have eight coordinate dodecahedral stereochemistry around molybdenum(VI) metal centre.