Assigning Ligand Redox Levels in Complexes of 2-Aminophenolates: Structural Signatures.

The purpose of this Viewpoint is to provide a broad-ranging update of advances in the coordination chemistry of redox-active (noninnocent) 2-aminophenolates, with emphasis on two ligand backbone structural parameters, the average of C-O and C-N (C-O/N) bond distances and Δa values, signifying the degree of bond-length alternation in the six-membered ring, in order to identify the redox level of the coordinated ligands. In the absence of magnetic, spectroscopic, and redox results, it has been established that it is possible to assign the electronic ground state of a coordination complex of 2-aminophenolates with consideration of charge, metal-ligand bond distances, and two very promising ligand backbone structural parameters. From a closer look at the sensitive ligand backbone metrical parameters of a diversified group of about 120 transition-metal complexes, a few very useful generalizations have been made.