Variable coordination behavior of rhodium metal complexes towards thiourea derivative ligands in comparison to its ruthenium and iridium analogs: Synthesis and biological studies

Reactions of arene d6 platinum group metal dimers [(arene)MCl2]2 (where M =Ru/Rh/Ir and arene = p-cymene, Cp*) with thiourea derivatives L1 {2-(3-methoxybenzoyl)-N-phenylhydrazinecarbothioamide}, L2 {2-benzoyl-Nphenylhydrazinecarbothioamide} and L3 {N-phenyl-2-(thiophene-2-carbonyl)hydrazinecarbothioamide} yielded a series of mononuclear neutral complexes (1-9) formulated as [(arene)M(L)k2(N & AND;S)Cl] {where L = L1, L2, L3, M =Ru, Ir, arene = p-cymene, Cp*} and [Cp*Rh(L)k1( S)Cl2] {where L = L1, L2, L3}. Further, treatment of monodentate rhodium complexes with sodium azide resulted in interesting dinuclear sulfur bridged complexes (10-12). These complexes have been characterized by various spectroscopic techniques such as FT-IR, UV-Vis, NMR spectroscopy and ESI-Mass spectrometry. The solid-state structures of the representative complexes determined by single-crystal X-ray diffraction studies showed that the ligands exhibit versatile coordination modes. In vitro antibacterial activity was evaluated against human pathogenic bacteria by the agar well diffusion method, which revealed their significant activity against both Gram-positive (Staphylococcus aureus and Bacillus thuringiensis) and Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria. Furthermore, antioxidant activity by DPPH assay revealed that the ligands and complexes are potent antioxidants.