Indium(III)-terpyridine complexes: synthesis, structures and remarkable antifungal and anticancer activities

Complexes of non-radioactive indium(III) with 2,2';6',2''-terpyridine (tpy) ligands have been rarely explored despite the popularity of tpy as a strong chelating ligand backbone. Herein, three mononuclear indium(III) complexes (In-1, In-2 and In-3) of tpy and its 4'-Cl and 4'-pyridyl derivatives have been synthesized and structurally characterized. While the crystal structure of In-1 has been previously studied, In-2 and In-3 were isolated and characterized for the first time. Two different polymorphs of In-2 were observed by simply varying the concentration of the reactants. Molecules of In-3 were determined by X-ray crystallography and found to adopt the same mononuclear coordination mode as that found in In-1 and In-2, while the remaining 4'-pyridyl ring was uncoordinated. Bioactivity studies revealed that indium(III) complexes In-1, In-2, and In-3 were fungicidal against the human fungal pathogen, Candida albicans, and several other non-albicans Candida species. Moreover, cytotoxicity studies showed these compounds were remarkably antiproliferative against human breast cancer cells (MCF-7 and MDA-MB 468).