Spin crossover in iron(ii) complexes with ferrocene-bearing triazole-pyridine ligands

Abstract

In the search for new multifunctional spin crossover molecular materials, here we describe the synthesis, crystal structures and magnetic and photomagnetic properties of the complexes trans-[Fe(Fc-tzpy)₂(NCX)₂]·CHCl₃ where Fc-tzpy is the ferrocene-appended ligand 4-(2-pyridyl)-1H-1,2,3-triazol-1-ylferrocene, X = S (1) and X = Se (2). Both complexes display thermal- and light-induced (LIESST) spin crossover properties characterised by T_1/2 = 85 and 168 K, ΔS = 55 and 66 J K⁻¹ mol⁻¹, ΔH = 4.7 and 11.1 kJ mol⁻¹ and T_LIESST = 47 K and 39 K for 1 and 2 respectively. The crystal structure of 1 and 2 measured at 275 K is consistent with the iron(II) ion in the high-spin state while the crystal structure of 2 at 120 K denotes the occurrence of complete transformation to the low-spin state.