This paper reports the isolation of a series of new coordination compounds formed with the terdentate ligand 2,4,6-tri(2′-pyridyl)-1,3,5-triazine (tpt) and various bivalent cobalt salts. The stereochemistries of these compounds are proposed after consideration of their elementary analyses, visible solid and solution spectra, infrared spectra, magnetic moments, and thermogravimetric studies. The chelates obtained include octahedral bis-complexes of the type [Co tpt2]X2 (where X = Cl, Br, I, CNS, ClO4, NO3, BF4, or BPh4) and five-coordinate mono-complexes of the type CoXz tpt (where X = Cl, Br, I, or NCS). A third dimeric form is also reported of general formula Co2X4 tpt, nH2O (where X = Cl, n = 0 or I; X = Br, n = 0 or 2). In this latter form the ligand appears to function as a composite of both terpyridine and bipyridine, showing simultaneous terdentate and bidentate behaviour, with one cobalt atom in either a five-coordinate or six-coordinate environment, and the other metal atom involved in tetrahedral coordination. In general the compounds formed are high-spin with normal room-temperature magnetic moments. The single exception is the red octahedral complex [Co tpt2]Cl2, 8.5H2O, which has a room-temperature moment of only 4.0 B.M.