Single-molecule magnets display magnetic bistability of molecular origin, which may one day be exploited in magnetic data storage devices. Recently it was realised that increasing the magnetic moment of polynuclear molecules does not automatically lead to a substantial increase in magnetic bistability. Attention has thus increasingly focussed on ions with large magnetic anisotropies, especially lanthanides. In spite of large effective energy barriers towards relaxation of the magnetic moment, this has so far not led to a big increase in magnetic bistability. Here we present a comprehensive study of a mononuclear, tetrahedrally coordinated cobalt(II) single-molecule magnet, which has a very high effective energy barrier and displays pronounced magnetic bistability. The combined experimental-theoretical approach enables an in-depth understanding of the origin of these favourable properties, which are shown to arise from a strong ligand field in combination with axial distortion. Our findings allow formulation of clear design principles for improved materials.

The field of multimetallic catalysis is rapidly developing and some multimetallic complexes catalyze organic transformations to yield the desired products in more efficient ways owing to the combined action of different metals in a cooperative fashion. This Concept article describes the recent advances of cooperative catalysis playing in multimetallic systems such as homo‐multimetallic complexes with short metal‐metal distances, homo‐multimetallic complexes with long metal‐metal distances, hetero‐multimetallic complexes and metallocene‐based multimetallic complexes with special attention towards redox‐switchable catalysis. Examples are illustrated in which the use of multimetallic complexes show clear enhancement of catalytic outcomes when compared with the sum of their corresponding mononuclear counterparts. Furthermore, several examples are discussed showing the effects of electronic communication in cooperative systems.