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

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 d(6) and d(7) complexes trans-[Fe-II(FTP)(2)(NCS)(2)] (1), [Co-II(FTTP)(2)](ClO4)(2)center dot 2(MeCN) (2) and [Fe-II(FTTP)(2)](ClO4)(2)center dot 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.