This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2015 New J. Chem. Cite this: DOI: 10.1039/c4nj02225d Lewis base controlled supramolecular architectures via non-covalent interactions of dioxomolybdenum( VI ) complexes with an ONS donor ligand: DFT calculations and biological study † Debanjana Biswal, a Nikhil Ranjan Pramanik,* b Syamal Chakrabarti,* a Nirmalya Chakraborty, c Krishnendu Acharya, c Sudhanshu Sekhar Mandal, a Saktiprosad Ghosh, a Michael G. B. Drew, d Tapan Kumar Mondal e and Sujan Biswas e Synthesis and characterization of five new mononuclear dioxomolybdenum(VI) complexes involving the Schiff base ligand (H 2 L) derived from 2-hydroxyacetophenone and S-benzyldithiocarbazate are reported. The ligand reacted with MoO 2 (acac) 2 and a monodentate Lewis base forming cis-dioxo Mo(VI) complexes of the type [MoO 2 LB] (where B = THF, 1-methylimidazole, 1-allylimidazole, g-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 p–p 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 mg per disc. They were also found to be effective antioxidants of the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical. Introduction Molybdenum is a versatile transition metal because it possesses a large number of stable and accessible oxidation states as well as coordination numbers which can vary from 4 to 8. The coordination chemistry of molybdenum plays an important role in industrial and biological reactions. Several industrial processes such as ammoxidation of propene, 1 olefin epoxidation 2a,b and olefin metathesis 3 reactions are carried out using molybdenum catalysts. The chemistry and the potentially useful biological activities of the Schiff base ligand derived from dithiocarbazates and their metal complexes have been investigated. 4–8 Diverse structural, stereochemical, spectroscopic and electrochemical properties manifested in its several coordination compounds in different oxidation states are also fascinating. Dioxomolyb- denum(VI) complexes containing the [MoO 2 ] 2+ core have been extensively studied due to their facile preparation, structural flexibility and stability. 9–13 The most interesting aspect of molyb- denum is its presence as molybdoenzymes catalyzing numerous vital biochemical reactions. The dioxomolybdenum(VI) complex with tridentate ONS donor ligands has received significant attention as providing a model system of the active site in molybdoenzymes such as xanthine oxidaze and sulfite oxidaze. 14–16 Similar types of Mo(VI) complexes have previously been reported by our research group, 17 but their structures were not determined by X-ray diffraction. As a continuation of these studies we have synthesized a tridentate ONS donor ligand derived from 2-hydroxyacetophenone and S-benzyldithiocarbazate (H 2 L) and a Department of Chemistry, University College of Science, 92, Acharya Prafulla Chandra Road, Kolkata 700009, West Bengal, India. E-mail: schakrabarti2014@gmail.com; Fax: +91-033-2351-9755; Tel: +91-033-2350-8386 b Department of Chemistry, Bidhannagar College, EB-2, Salt Lake, Kolkata 700064, India. E-mail: nr_pramanik@yahoo.co.in; Fax: +91-033-2337-4782; Tel: +91-033-2337-4389 c Molecular and Applied Mycology and Plant Pathology Laboratory, Department of Botany, University of Calcutta, Kolkata 700019, West Bengal, India d Department of Chemistry, The University of Reading, Whiteknights, Reading RG66AD, UK e Department of Chemistry (Inorganic section), Jadavpur University, Kolkata 700032, India † Electronic supplementary information (ESI) available: Supplementary Tables S1–S5 contain energy and composition of selected molecular orbitals of complexes 1–5 respectively. CCDC 1030098–1030103. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4nj02225d Received (in Victoria, Australia) 15th December 2014, Accepted 26th January 2015 DOI: 10.1039/c4nj02225d www.rsc.org/njc NJC PAPER Published on 09 February 2015. Downloaded by Calcutta University on 10/02/2015 08:50:06. View Article Online View Journal