Ferrocene-appended ligands for use in spin crossover-redox “hybrid” complexes of iron(ii) and cobalt(ii)

Abstract

In a study of multifunctional (‘hybrid’) molecular materials, with one function being spin-crossover and the second being reversible redox behaviour, we describe ferrocene-appended ligands and their d⁶ and d⁷ complexes trans-[Fe^II(FTP)₂(NCS)₂] (1), [Co^II(FTTP)₂](ClO₄)₂·2(MeCN) (2) and [Fe^II(FTTP)₂](ClO₄)₂·Et₂O (3) (where FTP = 4-(2-pyridyl)-1H-1,2,3-triazol-1-ylferrocene and FTTP = 4′-ferrocenyl-2,2′:6′,2′′-terpyridine). The structures, magnetism and solution electrochemistry are described. Complex 1 remains high-spin, 2 displays gradual, incomplete spin crossover and 3 remains low-spin between 350–2 K. The electrochemical results show that one-electron oxidations at the ferrocene group, located external to the coordination site, occur at more positive potentials than the ‘inner’ M^II/III couple in 1 and 2, but not in 3, and this has implications for retaining and influencing spin transitions at the M^II centres, in future.