Effects of Coordination to Transition Metals on the Hydration and Electroactivity of the Chelating Ligand 1,10-Phenanthroline-5,6-dione

The intrinsically electroactive ligand in the title was coordinated to Co 2+, Fe 2+, Ni 2+, Zn 2+, and Cu +, and the resulting hydration of the carbonyl groups of a portion of the coordinated ligand eliminated its electroactivity. The extent of hydration of the coordinated ligand was evaluated by means of rotating disk voltammetry. Estimates were obtained for the equilibrium constants governing the hydration reaction. The hydration induced by coordination of the ligand to the metal cations varied in parallel with the magnitude of the first association constant for the metal−ligand coordination.