The interplay between spin states, geometries and biological activity of Fe (III) and Mn(II) complexes with thiosemicarbazone

Fe(III) and Mn(II) complexes with condensation product of thiosemicarbazide and 2-acetylthiazole (HL1, (E)-2-(1-(thiazol-2-yl)ethylidene)hydrazine-1-carbothioamide) have been synthesized and characterized by single-crystal X-ray diffraction, IR spectroscopy, and elemental analysis. In both complexes, the thiosemicarbazone ligand is coordinated in deprotonated form through the NNS donor set of atoms. However, while Fe(III) complex is in the doublet ground state with distorted octahedral geometry, the coordination environment around Mn(II) is distorted trigonal-prismatic, and the sextet state is found to be the ground state. DFT calculations were performed to rationalize spin state preferences, and continuous shape measure describes the deviation from ideal six-coordinated polyhedral geometries in the ground and excited states. Antimicrobial activity (against a panel of Gram-negative and Gram-positive bacteria, two yeast, and one fungal strain), brine shrimp assay, and DPPH radical scavenging activity of both complexes were evaluated, and these results relate to the electronic structure of the complexes.

Automated summary

Fe(III) and Mn(II) complexes with a thiosemicarbazone ligand have been synthesized and characterized. The coordination environments and ground states of the complexes differ, with Fe(III) adopting a distorted octahedral geometry and a doublet ground state, while Mn(II) has a distorted trigonal-prismatic coordination environment and a sextet ground state. DFT calculations provide insights into the spin states, and the antimicrobial and antioxidant activities of the complexes correlate with their electronic structures.