Medicinal Utility of Thiosemicarbazones with Special Reference to Mixed Ligand and Mixed Metal Complexes: A Review.

Thiosemicarbazone complexes possess structural diversity and variable bonding patterns and potential biological implications and ion sensing abilities. The ability of the transition metals to acquire different geometries like octahedral, square planar and tetrahedral in different coordination environments has encouraged researchers to explore the coordination chemistry of thiosemicarbazone complexes which can also vary upon changing aldehydes and ketones, substituents attached to the carbonyl moiety, metal and its oxidation state, geometries, counter ions, presence of a solvent or additional molecules in the structures and substituents on the S or N(4)-atoms. This review aims to summarize recent developments in the synthesis and medicinal importance of thiosemicarbazone ligands and particular emphasis on their metal complexes. The mixed ligand-metal complexes have an important role to play in biological systems because a number of ligands try to combine with the same metal ions in vivo. Different ligands have different biological activities producing synergetic results and enhancing the potency of the formed complex. They also have a role to play in the storage and transport of substances, therefore the review article also covers the mixed ligand complexes of thiosemicarbazones with hetero ligands like 1,10-phenanthroline, pyridine, triphenyl phosphine etc. and their mechanistic action and medicinal benefits in recent years. The binuclear complexes of thiosemicarbazones with two different and same metal ions have also been explored here. Dinuclear complexes have been shown to possess interesting structures and in most cases, such complexes containing metal–metal bond also affects the complex's magnetic properties as well. It has been well discussed in the course of this study that metal complexes show enhanced biological activity than the free ligand or metal ion. The studies cited in the review have been sourced from publications indexed in known databases. Some of the recently explored structural alterations have been discussed in the paper and future substituted thiosemicarbazones and their complexes may emerge as multi-target inhibitors. [ABSTRACT FROM AUTHOR]