Equilibria in complexes ofN-heterocyclic molecules, part X. The pH dependent racemization of tris-(1,10-phenanthroline)nickel(II)

Abstract

SummaryCircular dichroism and electronic spectral measurements have established the existence of a covalent hydrate and a pseudobase arising from attack of H20 or HO-at the ligand in tris-(1,10-phenanthroline)nickel(ll). In anhydrous solvents and strongly acidic solution, the complex is largely unsolvated. Over a large pH range the dominant species present in aqueous solution is the covalent hydrate while at high pH, this is converted into the pseudo-base. The existence of these species, and the equilibria between them in aqueous solution elegantly explains the pH dependent dissociation and racemization of the parent molecule. It further explains the non-linear variation of these reactions in mixed solvents and indicates that more than one mechanism is responsible over the range of solvents studied here and previously.