The three novel heterotrimetallic complexes [Ni(H2L)(2)][CoCu(L)(2)((HL)-L-2)(NCS)(2)(NCS)(2) (1), [Ni(H2L)(2)][CuCo(L)(2)(H2L)(NCS)](2)Br-2.2H(2)O (2), and [CuCoCd(H2L)(2)(L)(2)(NCS)Br-2]-CH3OH (3) have been prepared using zerovalent copper; cobalt thiocyanate; nickel thiocyanate (1), nickel bromide (2), or cadmium bromide (3); and methanol solutions of diethanolamine in air. The most prominent feature of the structures of 1 and 2 is the formation of the "pentanuclear" aggregate {[Ni(H2L)(2)][CoCu(L)(2)(H2L)(NCS)]2}(2+) made up of two neutral [CoCu(L)(2)(H2L)(NCS)] units and the previously unknown cation [Ni(H2L)(2)](2+) "glued together" by strong complementary hydrogen bonds. With Cd2+ instead of Ni2+, a different structure is obtained: the [CoCu(L)(2)(H2L)(NCS)] unit is now linked to the Cd center through coordination of the oxygens of L groups on the Co atom to form the discrete heterotrimetallic molecular species 3. Cryomagnetic measurements of the compounds show that, in all cases, the magnetic behavior is paramagnetic; the polycrystalline EPR spectra contain signals due to monomeric copper species only. At the same time, the EPR spectra of frozen DMF and methanol solutions of 1-3 reveal the presence of triplet-state species that can be generated only by a coupling of the CU2+ centers within a dimer. The species responsible for the appearance of transitions within the triplet state are thought to be Cu(II) dimeric centers formed by aggregation of two {CuCo(H2L)(L)(2)} fragments of 1-3 present in solution. The residual monomeric spectra in the g approximate to 2 region are indicative of the existence of an equilibrium in solution between the dimeric and monomeric Cu(II) centers in aggregated and free {CuCo(H2L)(L)(2)} fragments, respectively, with varying degrees of stability. The fragmentation process of 1-3 in solution was screened by electrospray ionization mass spectrometry.