Magnetic susceptibility studies performed on 1 reveal a strongly antiferromagnetically coupled spin system. A near ideal Curie behavior was observed in the range of 50-270 K with a χT value of 1.90 emu K mol -1 (Fig 3A ), consistent with the expected spin-only value of 1.875 emu K mol -1 (g = 2) for an S = 3/2 spin state. Employing the Hamiltonian H = -2J(S1S2+S2S3), the data was fit with g = 2.00, J = -150 ± 20 cm -1 for T > 50 K. The subscripts in the Hamiltonian follow the numbering scheme for the Co centers in the crystal structure of 1 (Fig ). Due to the small curvature of the χT vs T curve, a relatively large variance of J is reported, and the fitted value should be taken as an estimate. However, the small temperature dependence of χT above 50 K suggests that the energy separation between the S = 3/2 ground state and the S = 1/2 and S = 5/2 excited states are on the order of several hundred wavenumbers. Below 50 K, χT decreases with temperature, and a zero-field splitting parameter of |D| = 6.7 cm -1 was used to fit the data. The thermally well-isolated S = 3/2 ground state of 1 is consistent with strong pair-wise antiferromagnetic exchange coupling between three high spin S = 3/2 Co II centers.