Unravelling interplay between molecule-based spin-state switching and electron transport in a single-crystal 3D metal-organic framework

Abstract Molecule-based Spin Crossover (SCO) materials display likely one of the most spectacular switchable processes. The SCO involves reversible changes in their physicochemical properties (i.e. optical, magnetic, electronic and elastic) that are coupled with the spin-state change under an external perturbation (i.e. temperature, light, magnetic field or the inclusion of analytes). Although very promising for their future integration into electronic devices, most of the SCO compounds show two major drawbacks: i) their intrinsic low conductance and ii) the unclear mechanism connecting the spin-state change and the electrical conductivity. Herein, we report the controlled single-crystal-to-single-crystal temperature-induced transformation in a robust metal-organic framework (MOF), [Fe2(H0,67bdt)3]·9H2O (1), being bdt2− = 1,4-benzeneditetrazolate, exhibiting a dynamic spin-state change concomitant with an increment in the anisotropic electrical conductance. 1 remains intact during the SCO process even after approximately a 15% volume reduction. The experimental and theoretical rationalization of the electronic orbital delocalization in the MOF points to a direct correlation between the spin-state of the iron and the electronic conductivity of the 3D structure.