Solvation/desolvation induced reversible distortion change and switching between spin crossover and single molecular magnet behaviour in a cobalt() complex

Coexistence and switching between spin-crossover (SCO) and single molecular magnet (SMM) behaviours in one single complex may lead to materials that exhibit bi-stable and stimuli sensitive properties in a wide temperature range and under multiple conditions; unfortunately, the conflict and dilemma in the principle of approaching SCO and SMM molecules make it particularly difficult; at low temperature, low spin (LS) SCO molecules possess highly symmetrical geometry and isotropic spins, which are not suitable for SMM behaviour. Herein, we overcome this issue by using a rationally designed Co( ii ) mononuclear complex [Co(MeOphterpy) 2 ] (ClO 4 ) 2 ( 1 ; MeOphterpy = 4′-(4-methoxyphenyl)-2,2′:6′,2′′-terpyridine), the magnetic properties of which reversibly respond to desolvation and solvation. The solvated structure reinforced a low distortion of the coordination sphere via hydrogen bonding between ligands and methanol molecules, while in the desolvated structure a methoxy group flipping occurred, increasing the distortion of the coordination sphere and stabilising the HS state at low temperature, which exhibited a field-induced slow magnetic relaxation, resulting in a reversible switching between SCO and SMM properties within one molecule. The cobalt( ii ) compound [Co(MeOphterpy) 2 ](ClO 4 ) 2 shows reversible switching between SCO and SMM properties depending on solvation or desolvation.