Synthesis and spectroscopic characterization of monometallic molybdenum (VI) complexes derived from bis(2-hydroxy-1-naphthaldehyde)succinoyldihydrazone

Molybdenum complexes [(μ2-O)2(MoO2)2(H4nsh)2]·2A·2C2H5OH (where A = O (1), py (2), 2-pic (3), 4-pic (4) and 5-pic (5)) have been synthesized in absolute ethanol from bis(2-hydroxy-1-naphthaldehyde)succinoyldihydrazone. The composition of the complexes has been deduced on the basis of the data obtained from elemental analyses and thermo-analytical data. All complexes are non-electrolyte in DMSO solution as evident from low value of molar conductance in the range 2.2–3.3 Ω−1 cm2 mol−1. The complexes are diamagnetic and have molybdenum in +6 oxidation state. The dihydrazone coordinates to the molybdenum centre as a neutral bidentate ligand through two azomethine nitrogen atoms only. This is revealed by the downfield shift of δ(CHN) signals by 0.16–0.44 ppm as compared to that in the free dihydrazone. The carbon atoms closer to azomethine nitrogen atoms downfield shift confirming the coordination of azomethine nitrogen atoms. The ν(CN) stretching vibrations also shift to lower frequency in the IR spectra of the complexes. Apart from the intra ligand bands, the complexes show a new absorption band in the region 421–423 nm attributed to charge-transfer transition from dihydrazone ligand to molybdenum centre. The dihydrazone is present in anti-cis conformation in all of the complexes. The complexes develop a new kind of intramolecular hydrogen bonding between naphtholic OH groups of coordinated dihydrazone.