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

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 T1/2 = 85 and 168 K, ΔS = 55 and 66 J K(-1) mol(-1), ΔH = 4.7 and 11.1 kJ mol(-1) and TLIESST = 47 K and 39 K for1 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 at 120 K denotes the occurrence of complete transformation to the low-spin state.