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(Fctzpy)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 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.
The research reported here was supported by the Spanish Ministerio de Economia y Competitividad (MINECO) and FEDER funds (CTQ2013-46275-P) and Generalitat Valenciana (PROMETEO/2012/049). T.R.M. and F.J.V.M. thank MINECO for a FPI grant. L.P.L. thanks the Generalitat Valenciana and the Universidad de Valencia for a predoctoral fellowship.