Variable-temperature (5-300 K) susceptibility measurements carried out for the binuclear nickel(II) complexes of a tetraamino diphenol macrocyclic ligand (H2L) of compositions [Ni2L(H2O)4](ClO4)2.4NH2CONH2 (1), [Ni2L(NCS)2(H2O)2].2Me2NCHO (2), [Ni2L(MeOH)2(ClO4)2].2NHEt3ClO4 (3), [Ni2L(im)2](ClO4)2 (4), [Ni2L(py)2](ClO4)2 (5), and [Ni2L(mu-O2CCH2NH3)(H2O)2](ClO4)2.2H2O (6) are reported. All the complexes behave antiferromagnetically, and the exchange parameter, J, varies in the following way : 1 (-17 cm-1), 2 (-21 cm-1), 3 (-29 cm-1), 4 (-50 cm-1), 5 (-67 cm-1), and 6 (-1 cm-1). The decrease in the value of J from 1 to 3 is attributed to the increase in tetragonal distortion around the metal centers. The change in stereochemistry of nickel(II) to the square pyramidal configuration leads to the significant decrease in the value of J for 4 and 5. The net effective exchange coupling constant of 6, in which two orthogonal superexchange pathways are involved, is very small. The X-ray structure of 2 has been determined. The complex crystallizes in the monoclinic space group P2(1)/c with a = 10.091(1) angstrom, b = 7.957(1) angstrom, c = 24.569(3) angstrom, beta = 92.77(1)-degrees, and Z = 2. The structure was solved by direct methods and refined to R = 0.039 and R(w) = 0.042. Complex 2 undergoes two reversible one-electron oxidation steps (E1/2 = 0.90, 1.05 V vs SCE, Pt/MeCN) with the formation of Ni(II)-Ni(III) and Ni(III)-Ni(III) species.