Crown ether bridged homo-and heterodinuclear copper(II) and nickel(II) cyclidene complexes interaction with anions

Abstract Homodinuclear ( 3CuCu , 3NiNi ) and heterdionuclear ( 3CuNi ) cyclidene complexes linked by two 1,10-diaza-18-crown-6 ethers were synthesized and their properties characterized. For the 3CuCu in the negative potential range the mixed-valence state Cu I –Cu II was observed and the comproportionation constants were determined. The redox potentials of M II/III showed a good correlation with DN of the solvent. In acetonitrile solution containing 0.1 mol dm −3 Bu 4 NPF 6 reversible M II/III redox processes were observed. However, in the presence of stronger ion pairing anions (e.g. BF 4 − and ClO 4 − ) the “potential inversion” occurred. Redox potentials of dinuclear complexes were compared with mononuclear cyclidene complexes. The influence of selected anions (Cl − and NO 3 − ) on the redox process M II/III was studied. The effect of Cl − anion was different for 3CuCu and 3NiNi . In 3CuCu coordination of two chloride anions took place after oxidation of copper centers. In the 3NiNi complex two Cl − anions were coordinated to one of the nickel(II) centers facilitating oxidation, at different potentials, of both nickel(II) cations. The behaviour of heteronuclear complex with Cl − anions was similar to 3NiNi . All dinuclear complexes interacted with NO 3 − anions and the observed potential shifts were larger for nickel(II) than for copper(II) cations.