Gradual spin crossover behavior encompassing room temperature in an Iron(II) complex based on heteroscorpionate ligand

In this paper, we report the synthesis of six novel triazol-based heteroscorpionate ligands based on heterocycle metathesis reactions and their Iron(II) complexes. Single crystal structural analyses, spectroscopic and magnetic properties of the obtained complexes were studied and their spin crossover-structural relationships compared to those obtained for their pyrazole-based analogues reported in the literature. In particular, the amino derivative complex Bis[hydrobis(pyrazol-1-yl)(3-amino-1,2,4-triazol-1-yl)]iron(II) obtained by post synthetic catalytic nitro-group reduction under pressure of hydrogen in an autoclave presents a scarce gradual spin crossover behavior encompassing room temperature. The profile of the SCO curve can be explain by the presence of only relatively weak H-bondings spreading only in one dimension. Among the interesting spin transition behaviors observed for the different complexes, such stable, complete and gradual spin crossover at room temperature makes this neutral complex a good candidate for sublimation and future investigation as active element notably for thermoreflectance-based surface microthermometry applications.