A series of binuclear nickel(II) complexes with one carboxylate bridge and two phenoxy bridges have been synthesized from a tetraamino diphenol macrocyclic ligand H(2)L. The perchlorate salts of the complex cation [Ni(2)L(mu-O(2)CR)(H2O)(2)](+) (R = H, CH3, C2H5, C3H5, or C6H5) have been spectroscopically characterized. All the complexes undergo reversible one-electron oxidation (CH3CN/Pt) at E(1/2)(1) = 0.80 V vs Ag/AgCl. Further oxidation of the butyrate and benzoate complexes take place nearly reversibly at E(1/2)(2) = 0.97 V. The crystal structure of [Ni(2)L(mu-O2CCH3)(H2O)(2)](ClO4).CH3OH.H2O has been determined : monoclinic, space group P2(1)/n; a = 10.621(1)Angstrom, b = 22.375(2) Angstrom, c = 14.411(2) Angstrom, beta = 107.39(1)degrees, Z = 4. The structure was solved by direct methods and refined to R = 0.049 and R(W) = 0.056. Variable-temperature (5-300 K) magnetic susceptibility measurements of the compounds show that they exhibit weak Ni Ni exchange interactions. The exchange coupling constant (J) varies in the following way : formate, -0.7 cm(-1); acetate, 2.9 cm(-1); propionate, 2.2 cm(-1); butyrate,0.5 cm(-1); and benzoate, 5.0 cm(-1).