ChemInform Abstract: Nickel(II) and Nickel(III) Bis(dipeptido) Complexes of α‐Aminoisobutyric Acid.

Abstract

ChemInform Abstract Ni(II) forms the high-spin complex (I) which changes at pH 9-11 to a low-spin form (II). Such a change of spin with pH is observed for dipeptides only when α-aminoisobutyric acid is in the second residue. This is attributed to the electron-donating ffect of the α-carbon methyl groups on the ligand field strength. (II) can be oxdidized, electrochemically or chemically, at pH 11 to a paramagnetic species (III), which is stable in neutral and basic solutions. A self-exchange rate constant is determined for the Ni(III)/Ni(II) ouple which is 500 times larger than values found for outer-sphere electron-transfer reactions of Ni(III)/Ni(II)-tripeptide complexes.