Four oxamato-bridged heterotrinuclear (NiCuNiII)-Cu-II-Ni-II complexes of formula {[Ni(bispictn)](2)Cv(pba)}(ClO4)(2).2.5H(2)O (I), {[Ni(bispictn)](2)Cu(pbaOH)}(ClO4)(2).H2O (2), {[Ni(cth)](2)Cu(pba)}(ClO4)(2) (3), and {[Ni(cth)](2)Cu(opba)}(ClO4)(2).H2O (4) and a binuclear (NiCuII)-Cu-II complex of formula [Cu(opba)Ni(cth)]. CH3OH (5) have been synthesized and characterized by means of elemental analysis, IR: ESR, and electronic spectra, where pba = 1,3-propylenebis-(oxamato), pbaOH = 2-hydroxyl-1,3-propylenebis(oxamato), opba = o-phenylenebis(oxamato), bispictn = N,N'-bis(2-pyridylmethyl)-1,3-propanediamine, and cth = rac-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane. The crystal structures of 1, 3, and 5 have been determined. The structures of complexes 1 and 3 consist of trinuclear cations and perchlorate anions,and that of 5 consists of neutral binuclear molecules which are connected by hydrogen bonds and pi-pi interactions to produce a unique supramolecular "double" sheet. In the three complexes, the copper atom in a square-planar or axially elongated octahedral environment and the nickel atom in a distorted octahedral environment are bridged by the oxamato groups, with Cu Ni separations between 5.29 and 5.33 Angstrom. The magnetic properties of all five complexes have been investigated. The X,MT Versus T plots for 1-4 exhibit the minimum characteristic of antiferromagnetically coupled NiCuNi species with an irregular spin state structure and a spin-quartet ground state. The chi T-M versus T plot for 5 is typical of an antiferromagnetically coupled NiCu pair with a spin-doublet ground state. The Ni-II-Cu-II isotropic; interaction parameters for the five complexes were evaluated and are between 102 and 108 cm(-1) ((H) over cap = -J (S) over cap (Cu).(S) over cap (Ni)).