Unusual High Thermal Stablility of a 2D → 3D Polycatenated Fe(II) Metal-Organic Framework Showing Guest-Dependent Spin-Crossover Behavior and High Spin-Transition Temperature

A novel three-dimensional (3D) Fe(II) metal-organic framework (MOF), [Fe-2(pptp)(4)center dot 2H(2)O](n), (1), constructed from the rigid 2-(3-(4-(pyridin-4-yl)pheny1)-1H-1,2,4-triazol-5-yOpyridine (Hpptp) ligand was synthesized and structurally characterized. Complex 1 exhibits a two-dimensional (2D) -> 3D polycatenated framework based on inclined interlocked 2D 4(4)-sql grids. Variable-temperature magnetic susceptibility measurements reveal that 1 is a rare example exhibiting a thermal-driven dehydration and consequently accompanied by a dramatic change of spin crossover (SCO) behaviors. Its spin transition temperature is as high as 390 K with similar to 20% high-spin character. Moreover, the framework of 1 shows unusual thermal stability to nearly 500 degrees C.