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

Preparation of the ligands HL1 = 2,6-[(N-phenylpiperazin-1-yl)methyl]-pethylphenol; HL2 = 2,6-[(N-phenylpiperazin-1-yl)methyl]-p-methoxyphenol and HL3 = 2,6-[(N-phenylpiperazin-1-yl)methyl]-p-nitrophenol are described together with their Cu(II) complexes with different bridging units. The exogenous bridges incorporated into the complexes are: hydroxo [Cu2L(OH)(H2O)2](ClO4)2.H2O (L1 = 1a, L2 = 1b, L3 = 1c), acetato [Cu2L(OAc)2]ClO4.H2O (L1 = 2a, L2 = 2b, L3 = 2c) and nitrito [Cu2L1(NO2)2(H2O)2]ClO4.H2O (L1 = 3a, L2 = 3b, L3 = 3c). Complexes 1a, 1b, 1c and 2a, 2b, 2c contain bridging exogenous groups, while 3a, 3b, 3c possess only open m-phenolate structures. Both the ligands and complexes were characterized by spectral studies. Cyclic voltammetric investigation of these complexes revealed that 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 ligand system, shifting to positive potentials when the substituents are replaced by more electrophilic groups. EPR studies indicate very weak interaction between the two copper atoms. Various covalency parameters have been calculated.