SYNTHESIS, SPECTRAL, MAGNETIC AND ELECTROCHEMICAL PROPERTIES OF NEW BINUCLEAR UNSYMMETRICAL AMINO-ACID LIGANDS AND THEIR CU(II) COMPLEXES WITH BRIDGING AND NON BRIDGING MOTIFS

The synthesis, spectral, magnetic and electrochemical properties of a series of binuclear Cu(II) complexes of new unsymmetrical binucleating ligands (H2L1, H2L2) are described where H2L1 = 4-methyl-2-[N-methyl piperazin-1-yl)methyl]-6-[(prolin-1-yl)-methyl] phenol and H2L2 = 4-br omo-2-[N-methyl piperazin-1-yl)methyl]-6-[(prolin-1-yl)]-methyl] pheno l. The exogenous ligands were incorporated into the complexes: hydroxo [Cu2L(OH)(H2O)(2)] ClO4. H2O (L-1 = 1a, L-2 = 1b), acetato, [Cu2L(OAc )(2)]. H2O (L-1 = 2a, L-2 = 2b), nitrito, [Cu-2(L(NO2)(2)(H2O)(2)] (L- 1 = 3a, L-2 = 3b), azido, [CuL(N-3)(2)]. 3H(2)O (L-1 = 4a, L-2 = 4b). Complexes 1a, 1b and 2a, 2b contain bridging exogenous groups, while 3 a, 3b and 4a, 4b possess only open mu-phenolato structures. Both, the ligands and complexes were characterised by spectral studies. The magn etic susceptibility of the complexes have been measured in the tempera ture range (77-300 K) and the exchange coupling parameter (2J) was det ermined from least square fitting of the data. The strength of the ant iferromagnetic interaction is in the order NO2 = N-3 > OAc > OH. The r edox behaviour of these complexes in acetonitrile reveal highly quasi reversible behaviour due to chemical or/ and stereochemical changes su bsequent to electron transfer. The first reduction potential is sensit ive to electronic effects of the substituents at the aromatic ring of the ligand system, shifting to positive potentials when the substituen ts are replaced by more electrophilic groups.