Molecular weight measurements and the visible absorption spectra of mixed solutions of Tb(aa)3 3H2O and Co(aa)2 in benzene indicate that these complexes interact to form mixed metal oligomeric species. The slow decrease in Tb3+ ion phosphorescence after mixing the individual solutions supports this interpretation. Similar investigations with Ni(aa)2 also provide evidence for mixed metal oligomeric complexes. Crystalline compounds with analyses corresponding to the stoichiometries CoTb(aa)53H2O and NiTb(aa)53H2O have been isolated from benzene solution.