Synthesis and physiochemical studies on binuclear Cu(II) complexes derivedfrom 2,6-[(N-phenylpiperazin-1-yl)methyl]-4-substituted phenols

Preparation of the ligands HL1 = 2,6-[(N-phenylpiperazin-1-yl)metllyl]-p-et hylphenol; HL2 = 2,6-[(N-phenylpiperazin-1-yl)methyl]-p-methoxyphenol and H L3 = 2,6-[(N-phenylpiperazin-1-yl)methyl]-p-nitrophenol arc described toget her with their Cu(II) complexes with different bridging units. The exogenou s bridges incorporated into the complexes are: hydroxo [Cu2L(OH)(H2O)(2)](C lO4)(2).H2O (L-1 = 1a, L-2 = 1b, L-3 = 1c), acetato [Cu2L(OAc)(2)]ClO4.H2O (L-1 = 2a, L-2 = 2b, L-3 = 2c) and nitrito [Cu2L1(NO2)(2)(H2O)(2)]ClO4.H2O (L-1 = 3a, L-2 = 3b, L-3 = 3c). Complexes la, 1b, le and 2a, 2b, 2c contain bridging exogenous groups, while 3a, 3b, 3c possess only open mu -phenolat e structures. Both the ligands and complexes were characterized by spectral studies. Cyclic voltammetric investigation of these complexes revealed tha t the reaction process involves two successive quasireversible one-electron steps at different potentials. The First reduction potential is sensitive to electronic effects of the substituents at the aromatic ring of the ligan d system, shifting to positive potentials when the substituents are replace d by more electrophilic groups. EPR studies indicate very weak interaction between the two copper atoms. Various covalency parameters have been calcul ated.