Photo- and Electronically Switchable Spin-Crossover Iron(II) Metal-Organic Frameworks Based on a Tetrathiafulvalene Ligand

A major challenge is the development of multifunctional metal-organic frameworks (MOFs), wherein magnetic and electronic functionality can be controlled simultaneously. Herein, we rationally construct two 3D MOFs by introducing the redox active ligand tetra(4-pyridyl) tetrathiafulvalene (TTF-(py)(4)) and spin-crossover FeII centers. The materials exhibit redox activity, in addition to thermally and photo-induced spin crossover (SCO). A crystal-to-crystal transformation induced by I-2 doping has also been observed and the resulting intercalated structure determined. The conductivity could be significantly enhanced (up to 3 orders of magnitude) by modulating the electronic state of the framework via oxidative doping; SCO behavior was also modified and the photomagnetic behavior was switched off. This work provides a new strategy to tune the spin state and conductivity of framework materials through guest-induced redox-state switching.