An Iron(Ii) Spin Crossover Complex With A Maleonitrile Schiff Base-Like Ligand And Scan Rate-Dependent Hysteresis Above Room Temperature

A Schiff base-like ligand bearing a maleonitrile backbone was synthesized and converted in two steps to an octahedral iron(II) complex with axial imidazole ligands. Single crystal X-ray structure analysis of this complex revealed a 3D hydrogen bond network based on the NH groups of the axial imidazole ligands that act as donors. Interestingly, temperature-dependent magnetic measurements showed an abrupt spin crossover with hysteresis above room temperature. Thereby, the hysteresis width features a strong scan rate dependency leading to a 6 K wide hysteresis at a scan rate of 5 K/min and 1 K width when measured in settle mode. This kinetic effect is further investigated by DSC measurements verifying the strong scan rate dependency of the hysteresis width. The small hysteresis was additionally followed using temperature-dependent PXRD. For comparison, the corresponding pyridine complex was synthesized as well.