Control of iron(II) spin states in 2,2′:6′,2″-terpyridine complexes through ligand substitution

Abstract

A series of 6-and 6,6″-arylsubstituted 2,2′:6′,2″-terpyridine ligands and their iron(II) complexes have been prepared. The introduction of phenyl substituents at both the 6-and 6″-positions leads exclusively to the formation of orange high-spin iron(II) complexes whilst the presence of a single 6-phenyl substituent results in spincrossover systems. The complexes [Fe(2)2]X2 (2 = 4,6-diphenyl-2,2′:6′,2″-terpyridine; X = ClO4 or PF6) have been studied in detail, and the solid-state X-ray structures of both the low-and high-spin forms are reported. Mössbauer spectroscopic and magnetic susceptibility measurements are reported, and the temperature and pressure dependence of the high-spin/low-spin transition have been studied. An X-ray structural study of the complex [Fe(2)2](ClO4)2 is also reported; this complex is highly distorted with two very long Fe ⋯ N contacts of over 2.4 Å and is best regarded as a four-coordinate iron complex.