Self-assembly of a supramolecular spin-crossover tetrahedron

Abstract

Spin-crossover (SCO) compounds are fascinating switchable materials with great potential for the development of novel technological devices. These coordination complexes exhibit metal ions with two possible electronic configurations (low- spin, LS, and high-spin, HS) which can be toggled using exter- nal stimuli such as temperature, pressure, or light irradiation. The different magnetic, optical, and structural features of the two states allow these materials to be exploited for a wide range of applications, such as sensors, actuators, or for information storage. Interestingly, the physical pro- perties of SCO compounds can be tuned by modifying the weak non-covalent interactions exhibited within or in between their molecular entities. In host–guest systems, these inter- actions offer a versatile tool, for example, for manipulating the transition temperature of encapsulating SCO complexes simply by altering the nature of the supramolecular guest, as shown in dinuclear helicates, tetrahedral cages, or cubic architec- tures. Long range intermolecular interactions can be exploited as well to tune or even to activate/deactivate the SCO behaviour. Such modulation arises from the nature and strength of such interaction, which influence the communi- cation between molecules and thus its cooperativity, or affect the ligand field exerted by the donor set and therefore the SCO temperature.