Effect of azide co-ligand on the crystal structures of rhodium and iridium metal complexes featuring pyridine-based thiourea derivatives: Characterization and in vitro biological studies

• Strained four- and stable six-membered к 2 (N, S) -L azido complexes were synthesized. • Ligand L3 and its complexes 7 and 8 exhibit active antibacterial activity. • The molecular structures of these complexes were confirmed by X-ray diffraction. Half-sandwich rhodium and iridium metal complexes 1 – 4 were prepared by the reaction of the pyridine-based thiourea-derived ligands with rhodium and iridium metal dimers. Iridium complex 1 yielded a mono-dentate S bonded complex whereas others formed bidentate NS complexes 2 – 4 . These complexes were further treated with NaN 3 in methanol. Treatment of the monodentate complex 1 with NaN 3 resulted in the formation of highly strained four-membered к 2 (N, S) -L azido complex 5 , whereas the reaction of the bidentate complexes 2 – 4 afforded stable six-membered к 2 (N, S) -L azido complexes 6 – 8 . The general formula for these complexes can be formulated as [Cp*M(к 2 (N, S) -L)N 3 ] where M = Rh/Ir, L = thiourea ligand. These metal complexes have been characterized by different spectroscopic techniques and their molecular structures have been confirmed by single-crystal X-ray study. All these azido complexes were isolated as air-stable bright red crystals and crystallized in a triclinic crystal system with space group P. Preliminary antibacterial and antioxidant screenings on the ligands and complexes show that they exhibit significant antibacterial activity and minimal antioxidant activity.