Spin Crossover-Assisted Modulation of Electron Transport in a Single-Crystal 3D Metal-Organic Framework

Molecule-based spin crossover (SCO) materials displaylikely oneof the most spectacular switchable processes. The SCO involves reversiblechanges in their physicochemical properties (i.e. optical, magnetic,electronic, and elastic) that are coupled with the spin-state changeunder an external perturbation (i.e. temperature, light, magneticfield, or the inclusion/release of analytes). Although very promisingfor their future integration into electronic devices, most SCO compoundsshow two major drawbacks: (i) their intrinsic low conductance and(ii) the unclear mechanism connecting the spin-state change and theelectrical conductivity. Herein, we report the controlled single-crystal-to-single-crystaltemperature-induced transformation in a robust metal-organicframework, [Fe-2(H(0.67)bdt)(3)]& BULL;9H(2)O (1), being bdt(2-) = 1,4-benzeneditetrazolate,exhibiting a dynamic spin-state change concomitant with an incrementin the anisotropic electrical conductance. Compound 1 remains intact during the SCO process even after approximately a15% volume reduction. The experimental findings are rationalized byanalyzing the electronic delocalization of the frontier states bymeans of density-functional theory calculations. The results pointto a correlation between the spin-state of the iron and the electronicconductivity of the 3D structure. In addition, the reversibility ofthe process is proved.