Spin crossover-assisted modulation of 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/release of analytes). Although very promising for their future integration into electronic devices, most 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, [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. Compound 1 remains intact during the SCO process even after approximately a 15% volume reduction. The experimental findings are rationalized by analyzing the electronic delocalization of the frontier states by means of density-functional theory calculations. The results point to a correlation between the spin-state of the iron and the electronic conductivity of the 3D structure. In addition, the reversibility of the process is proved.