A Multifunctional [CoII4L4] Molecular Cage: Coexistence of Spin-State Switching and Slow Magnetic Relaxation

A discrete cobalt(II) tetrahedral molecular cage [CoII4L4]8+ (1) (L: C3 symmetric tris-bidentate ligand) was synthesized via self-assembly metal ion assisted process with ligand L. The cage was structurally characterized by single crystal X-ray diffraction, 1H-NMR and ESI-MS spectroscopy studies. In solid state, all four cobalt(II) centers remain in the high-spin states, whereas solution-state NMR spectroscopy reveals the presence of two high-spin cobalt(II) and two low-spin cobalt(II) centers at room temperature. Variable temperature 1H-NMR shows the onset of gradual spin crossover above 350 K. Realizing spin-state switching in solution is a rare and noteworthy accomplishment in the context of cobalt(II) cage architectures of the [M₄L₄]ⁿ⁺ type. Also, 1 showed the field induced slow relaxation of magnetization at low temperature