Spin-Crossover In An Iron(Iii) Complex Showing A Broad Thermal Hysteresis

A pentadentate Schiff-base ligand Cl-3,Cl-5-L2- and NCSe- form an iron(iii) mononuclear complex, namely [Fe(Cl-3,Cl-5-L)(NCSe)], which shows a thermally induced spin crossover with a broad hysteresis width of 24 K between 123 K (warming) and 99 K (cooling). Analogous complexes of the [Fe(X-3,X-5-L)(Y)] type, where X = Cl or Br and Y = Cl-, N-3(-), NCS-, and NCSe-, are high-spin over the whole temperature interval.