Assembling Smallest Prussian Blue Analogs Using Chiral Hydrogen Bond-Donating Unit toward Complete Phase Transition.

Exploring methods for assembling functional materials at the molecular level may yield functional expressions derived from the assembly method. This study developed novel switchable molecular assemblies characterized by abrupt, complete phase transitions promoted via hydrogen bonding with a chiral carboxylic acid. These assemblies were prepared by aggregating discrete molecules that are unresponsive to external stimuli. Furthermore, enantiopure hydrogen-bond donor (HBD) molecules provide switchable compounds with cooperative and abrupt phase transitions, whereas the racemic mixture of the HBD provides a hydrogen-bonded one-dimensional compound with a broad and incomplete phase transition when structural disordering is observed. This study presents a novel strategy for observing metal-to-metal electron-transfer-coupled spin transitions via hydrogen-bond formation.

Solvation/desolvation induced reversible distortion change and switching between spin crossover and single molecular magnet behaviour in a cobalt(II) 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] (ClO4)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.