Synthesis, characterisation and crystal structure of cis-dioxomolybdenum(VI) complexes of some potentially pentadentate but functionally tridentate (ONS) donor ligands

Neutral cis-dioxomolybdenum(VI) complexes with potentially pentadentate ONSNO donor Schiff bases of thiocarbodihydrazone of salicylaldehyde (H3L1), 5-bromo (H3L2), 5-nitro salicylaldehyde (H3L3) and 2-hydroxyacetophenone (H3L4) acting as tridentate ONS donor ligands have been synthesised. The complexes are found to be of the form MoO2LH(R-OH) (R = CH3) where, LH = (LH)-H-1, (LH)-H-2, (LH)-H-3 and (LH)-H-4. The complexes were characterised by elemental analyses, UV, IR, and H-1 NMR spectroscopy, magnetic susceptibility measurement, molar conductivities in solution and by cyclic voltammetry. Two of the complexes [MoO2((LH)-H-2)(MeOH)] and [MoO2((LH)-H-4)(MeOH)] were crystallographically characterised. The structures reveal that the molybdenum acceptor centre is present in a distorted octahedral NO4S donor environment. The presence of a substituent either on the aromatic ring of the salicylaldehyde moiety or on the carbon atom of its carbonyl group is found to exhibit little effect on the corresponding metal ligand bond distances and angles. The sixth coordination site of the complexes harboring the weakly coordinated R-OH moiety is found to act as the binding site for various neutral monodentate Lewis bases. (C) 2002 Elsevier Science Ltd. All rights reserved.