Multistability at Room Temperature in a Bent-Shaped Spin-Crossover Complex Decorated with Long Alkyl Chains

An iron(II) pyridyl-benzohydrazonate-based complex decorated with long alkyl chains is reported as a rare spin-crossover compound displaying a wide thermal hysteresis spanning room temperature. On heating, this compound exhibits a spin transition between a LS ground state and an ordered HS-LS phase with symmetry breaking from monoclinic P2(1)/n into orthorhombic P2(1)2(1)2 space groups. During cooling, the compound first transits into a magnetically distinguishable HS-LS phase with monoclinic P2(1) symmetry before returning into the LS phase. Interconversion between the two distinct HS-LS phases is the result of subtle structural changes in the alkyl chains and produces a second minor thermal hysteresis that superposes to the large one. This unprecedented result shows that the combination of a conventional cooperative spin transition and ligand-driven magnetic changes can promote magnetic tristability at room temperature.