Transfer of Discrete Spin Crossover Complexes into Structurally Infinite Architectures using the Metalloligand Approach

High-density data storage systems, molecular switches and other spintronic devices show promise for application in the next generation of electronics; however, precise control of electronic states in extended architectures remains a significant challenge. Spin crossover (SCO) materials are promising candidates for the development of such devices due to their intrinsic electronic and magnetic bistability. In this context, the use of pre-existing SCO complexes as building blocks to generate extended coordination polymer (CP)/metal-organic framework (MOF)-type architectures remains largely unexplored, owing to the difficulty of preserving SCO behavior following network formation. To this end, we now demonstrate the use of the metalloligand approach as a general strategy for enabling the transfer of SCO behaviors into new extended CP/MOF architectures following the coordination of Ag(I) ions to the secondary coordination domains of the parent metalloligand. In general, integration of the parent metalloligand, [FeL](BF4)2 (where L = tris((((1-(pyridin-4-yl)-1H-imidazole-4-yl)methylene)amino)ethyl)ethane-1,2-diamine), in this fashion was found to enhance cooperativity and structural robustness by introducing additional metal-ligand and ligand-ligand interactions. Detailed structure-function relationships for various solvatomorphs of the parent metalloligand highlight potential mechanisms of action altering both the completeness and cooperativity of the corresponding spin-profiles. Further, structural augmentation of the parent metalloligand enables additional tunability of the SCO behavior following simple variation of the secondary metal ion species. This work reports a general strategy for the rational design of multifunctional SCO materials and represents, to the best of our knowledge, a very rare demonstration of the transfer of a SCO metalloligand into SCO-active CP/MOF-type architectures.