Reversible On-Off Switching of the Hysteretic Spin Crossover in a Cobalt(II) Complex via Crystal to Crystal Transformation.

Reversible controlling and switching of magnetic bistability remains relatively difficult. Here, reversible on-off switching of a hysteretic spin transition in a CoII complex via a single-crystal to single-crystal (SC-SC) transformation during dehydration and rehydration was reported. Upon dehydration, a switching from a basically low spin state to an abrupt and hysteretic spin crossover (SCO) with broad hysteresis loops was achieved. Hysteretic and anisotropic crystal lattice expansion or contraction in the spin transition temperature range was also observed in the dehydrated complex. The magneto-structural relationship in this system was established on the basis of detailed structure analyses on both the hydrated and dehydrated examples over a wide range of temperatures. The elimination of guest internal pressure, the tuning of the supramolecular interactions, and the strong electron-lattice coupling should be responsible for the hysteretic SCO in the dehydrated complex.