A macrocyclic tetramine-diphenol Ligand (H(2)L(2)) with two different cavity sizes provided by an ethylene and propylene bridge, respectively, between the two sets of amine groups, on reaction with VO(acac)(2) produces a mixture of monomeric oxovanadium(IV) and -(V) complexes of the [L(2)](2-) anion. This mixture reacts with nickel(II) perchlorate and affords three compounds of composition [((VO)-O-IV)L(2)Ni(H2O)(2)] (ClO4)(2) (4), [{((VO)-O-IV)L(2)Ni(H2O)}{((VO2)-O-V)(HL(2))}](ClO4)(2) . 3H(2)0 . 2 . 5CH(3)OH (5) and [NiL(2)((VO)-O-IV)](ClO4)(2) (6). Complex 4 reacts with pyridine to produce [((VO)-O-IV)L(2)Ni(py)](ClO4)(2) . H2O (7). The coordination geometry of nickel is octahedral in 4 and 5, square planar in 6, and square pyramidal in 7. Vanadyl(IV) sulfate on reaction with H(2)L(2) affords [((VO)-O-IV)(H(2)L(2))(SO4)]. 5H(2)O (8) as the sole product, in which both of the amino nitrogens of the -NH(CH2)(2)NH- moiety are protonated. Complex 8 reacts with Ni(acac)(2) to produce [NiL(2)((VO)-O-IV)(SO4)]. H2O (10), in which the nickel is square planar. Complexes 4, 6, 7, and 10 exhibit geometrical and positional isomerism. The cyclic voltammograms for 6, 8, [((VO)-O-IV)H(2)L(2)](NO3)(2) . 2H(2)O (9) and 10 exhibit a redox couple due to (VO)-O-IV --> (VO)-O-V oxidation in all the cases. The six-coordinate oxovanadium complexes 8 and 10 undergo more facile oxidation (E(1/2) = 0.57 V vs Ag/AgCl) relative to the five-coordinate species 6 and 9 (E(1/2) = 0.80 V) Complexes 4, 5, and 7 behave ferromagnetically and the exchange coupling constants (J) for these compounds are as follows : 12 cm(-1) (4); 2 cm(-1) (5); 5 cm(-1) (7). The crystal structure of the mixed-valence heterotrinuclear complex 5 has been determined. Crystal data for 5 : monoclinic; space group P2(1)/c; a = 16.611(8) Angstrom, b = 15.266(5) Angstrom, c = 24.880(4) Angstrom, beta = 95.93(2)degrees, V = 6275(4) Angstrom(3), Z = 4; R = 0.069, wR(2) = 0.183.