Cationic cobaltammines as anion receptors: Sonochemical synthesis, characterization and comparative account of antibacterial activity of nano and non-nano pentaammineazidocoablt(III) compounds

Abstract

Sonochemical technique has lead the synthesis of nano-scale cobalt(III) compounds from pentaammineazidocobalt(III) chloride and sodium salts of metal oxoanions (Na2MO4·2H2O, M = Mo or W) in an aqueous medium. These dark red coloured particles have composition [Co(NH3)5N3]MO4 (M = Mo or W) and further characterization by UV–Vis, IR, SEM, Zeta-sizer and PXRD. Through classical method their crystals have also been grown and their characterization has been done by UV–Vis, IR, PXRD and SCXRD. Thermal stability of single crystalline and nano-scale cobalt(III) compounds have been determined by thermal gravimetric analysis. The binding ability of pentaammineazidocobalt(III) cation for oxoanions has been observed (in an aqueous solution) with UV–Vis spectroscopic titrations (log k = 2.35 (MoO42-), 3.76 (WO42-). Single crystal X-ray structures of both the compounds have revealed the presence of one cation and one anion. Electrostatic forces of attraction and strong H-bonding interactions (NH…O) have stabilized crystal lattices in both the structures. All compounds along with sodium salts of oxoanions has further revealed their antibacterial activities using a strain of gram negative bacteria, a strain of gram positive bacteria and acid fast bacteria (Escherichia coli,Bacillus thuringiensis and Mycobacterium smegmatis respectively). This study predicts that these new nano compounds have two-fold more inhibitory activity as compared to the normal crystalline compounds and sodium salts of oxoanions.