Sudhanshu Sekhar Mandal

Chemical, electrochemical and structural studies of some cis -dioxomolybdenum(VI) complexes of two tridentate ONS chelating ligands

Several cis-dioxomolybdenum complexes of two tridentate ONS chelating ligands H2L1 and H2L2 (obtained by condensation of S-benzyl and S-methyl dithiocarbazates with 2-hydroxyacetophenone) have been prepared and characterized. Complexes 1 and 2 are found to be of the form MoO2 (CH3OH) L1 · CH3OH and MoO2L, respectively, (where L2– = dianion of H2L1 and H2L2). The sixth coordination site of the complexes acts as a binding site for various neutral monodentate Lewis bases, B, forming complexes 3–10 of the type MoO2LB (where B = γ-picoline, imidazole, thiophene, THF). The complexes were characterized by elemental analyses, various spectroscopic techniques, (UV-Vis, IR and 1H NMR), measurement of magnetic susceptibility at room temperature, molar conductivity in solution and by cyclic voltammetry. Two of the complexes MoO2(CH3OH) L1 · CH3OH (1) and MoO2L1(imz) (5) were structurally characterized by single crystal X-ray diffraction. Oxo abstruction reactions of 1 and 5 led to formation of oxomolybdenum(IV) complex of the MoOL type.

Synthesis, chemical, and electrochemical studies of oxomolybdenum(IV) complexes with two tridentate ONS donor ligands

This manuscript reports the synthesis, characterization, chemical, and electrochemical studies of several oxomolybdenum (IV) complexes of tridentate ONS donor ligands obtained by the condensation of 2-hydroxyacetophenone with S-benzyl and S-methyl dithiocarbazates. The complexes are of the forms [MoIVOL] and [MoIVOL(N–N)], where N–N = 2,2′-bipyridine and 1,10-phenanthroline, derived from the corresponding [MoO2L] complexes through oxo abstraction by triphenylphosphine in the absence/presence of N–N bidentate donors. Electrochemical behavior of these complexes have been investigated for insight into the redox behavior of the Mo(IV) centers of these complexes.

Lewis base controlled supramolecular architectures via non-covalent interactions of dioxomolybdenum(VI) complexes with an ONS donor ligand: DFT calculations and biological study

Synthesis and characterization of five new mononuclear dioxomolybdenum(VI) complexes involving the Schiff base ligand (H2L) derived from 2-hydroxyacetophenone and S-benzyldithiocarbazate are reported. The ligand reacted with MoO2(acac)2 and a monodentate Lewis base forming cis-dioxo Mo(VI) complexes of the type [MoO2LB] (where B = THF, 1-methylimidazole, 1-allylimidazole, γ-picoline and pyridine). In all the complexes the ligand is coordinated to molybdenum via tridentate ONS donors phenolic oxygen, imine nitrogen and thioenolate sulfur. The crystal structures of the ligand and the five complexes have been determined by single crystal X-ray crystallography. These complexes are neutral with the metal having distorted octahedral geometry. All the complexes give rise to fascinating supramolecular architectures via hydrogen bonding and π–π stacking interactions. DFT calculations on the ligand and complexes are also carried out. The Schiff base ligand and its dioxomolybdenum(VI) complexes were tested against five human pathogenic bacteria Bacillus cereus, Bacillus subtilis, Proteus vulgaris, Escherichia coli, Pseudomonas aeruginosa and a fungi Candida albicans to assess their efficiency as antimicrobial agents. The MIC (minimum inhibitory concentration) for antimicrobial activity ranges from 1.0–10.0 μg per disc. They were also found to be effective antioxidants of the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical.

Synthesis, chemical and electrochemical studies of complexes of a tridentate ONS chelating ligand built around the elusive [MoVIOS]2+ core

Synthesis and characterization of four Mo(VI) complexes of a diprotic tridentate ONS chelating ligand (H2L) containing the rather elusive [MoVIOS]2+ core is reported. These [MoVIOSL] complexes are obtained from their corresponding [MoVIO2L] precursors using a combination of PPh3 and PPh3S. This process of oxo-abstraction and sulfido-inclusion affected by PPh3–PPh3S is reported for the first time and may be considered as a general method of converting [MoVIO2L] complexes to the corresponding [MoVIOSL] complexes. Direct structural characterization of these complexes could not be done due to the ease of solvolysis of these oxosulfidomolybdenum(VI) complexes to the corresponding dioxomolybdenum(VI) analogues. However, the structure of these [MoVIOSL] complexes could be reasonably surmised from the corresponding structurally characterized [MoVIO2L] complexes. Points of attachment of the potentially pentadentate but functionally tridentate ONS chelating ligands to [MoVIOS]2+ are located mainly through analysis of IR and UV-Vis spectral data and comparison with corresponding [MoVIO2L] complexes of known structure. Conditions under which solvolysis of [MoVIOS]2+ to the [MoVIO2]2+ core is significantly retarded have been identified and make us hopeful of obtaining single crystals of [MoVIOSL].

Synthesis, chemical, electrochemical, and structural characterization of binuclear dioxo-bridged molybdenum(VI) complexes of tridentate ONS donors

A number of dioxo-bridged binuclear molybdenum(VI) complexes with diprotic tridentate ONS donor Schiff bases (H2L1, H2L2, H2L3, and H2L4) obtained by the condensation of salicylaldehyde/2-hydroxyacetophenone with S-benzyl and S-methyl dithiocarbazates have been synthesized using the Mo(V) complex (NH4)2[MoVOCl5] as starting material. All these reactions are carried out in air and the MoVO center of the precursor complex undergoes spontaneous aerial oxidation leading to the formation and isolation of molybdenum(VI) complexes Mo2O4L2. The complexes were characterized by elemental analyses, various spectroscopic techniques (UV-Vis, infrared etc.), magnetic susceptibility at room temperature, molar conductivity, and cyclic voltammetry. One of the complexes, Mo2O4L2 1 (1), was structurally characterized by single-crystal X-ray crystallography.