Structure and electrochemistry of salen type cerium (IV) complexes tuned by multiform counterions

Reactions of N,N′-bis(2-oxy-3-methoxybenzylidene)-1,2-phenylenediamine (H2L) with different cerium salts, e.g. Ce(OAc)3·5H2O, Ce(NO3)3·6H2O and CeCl3·6H2O, afford three salen type mononuclear Ce(IV) complexes, namely, [Ce(IV)(L)2]·2CH2Cl2 (1), [Ce(IV)(L)2] (2) and (NH4)2[Ce(IV)(L)2](PF6)2 (3). X-ray crystallographic analysis reveals that complexes 1 and 3 are of distorted sandwich mononuclear structures, while complex 2 is of a crossover mononuclear structure. All Ce(IV) ions are eight-coordinated to four imines nitrogen atoms and four oxygen atoms of phenolic hydroxyl groups from two ligands. Complexes 1–3 represent few known salen type cerium complexes with Ce(IV) ions. Cyclic voltammograms and differential pulse voltammograms of complexes 1–3 show a reversible one-electron oxidation and a reversible one-electron reduction within the electrochemical window of CH3CN.