Metal Complexes of Ligand Radicals: In Pursuit of Ligand Non-Innocence

Mukhopadhyay, Narottam (2023) Metal Complexes of Ligand Radicals: In Pursuit of Ligand Non-Innocence. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Narottam Mukhopadhyay (14RS044)) 14RS044.pdf - Submitted Version Restricted to Repository staff only Download (16MB)

Abstract

The interplay of transition metal ions with redox-active proradical ligands and the correlation of reactivity with electronic structure is an area of significant current research interest. Because of their redox-active character, these ligands profoundly influence the electronic structural properties of the resulting complexes. 2-aminophenolates and 1,2-phenylenediamide are prototypical redox-active ligands whose ability to span oxidation levels range from dianionic to monoanionic (semiquinonate radical) to neutral (quinone) forms, allowing them to store redox equivalents. The research work presented in this thesis describes the exhaustive coordination chemistry of selected first-row transition-metal ions with the deprotonated form of a newly synthesized redox-active ligand H3L¹. H3L¹ is a pyridine-2-carboxamide appended fused 1,2-phenylenediamide and 2-aminophenolate-based tetradentate ligand. In its deprotonated form, while the amide part is expected to stabilize the higher oxidation state of metal ions, the spacer phenylenediamide and 2-aminophenolate units are proradical in nature. This typical nature provides an asymmetry in the coordination and electronic properties of the said ligand. Detailed synthetic protocols for a series of coordination complexes with Ni(II), Cu(II), Mn(II), Fe(III), and Zn(II) have been described. In these complexes, the coordinated ligand not only attains its various accessible redox levels but also goes through an unprecedented ligand-centered redox-driven cyclization in the fused 1,2-phenylenediamide and 2-aminophenolate part to yield a new redox-active phenoxazinylate core. Ligand field perturbed interesting spin-induced phenomena like valance-tautomerism, partial spin crossover (SCO), and complete spin switchover have also been noticed in those complexes. Detailed experimental investigations and their appropriate rationalization with the help of theoretical calculations have been done to achieve a deeper electronic-level understanding. The comprehensive explorations of various metal complexes with a common ligand helped to perceive the true non-innocent character of a redox-active ligand.

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