The effect of steric hindrance on the Fe(II) complexes of triazine-containing ligands

Fe(II) complexes based on ligands containing a 1,3,5-triazine core have been synthesised and characterised and their electrochemical, spectroscopic and magnetic properties have also been investigated. The incorporation of various substituted metal-binding heterocycles into the 2,4-positions of the triazine allows the properties of the complexes to be modified considerably. Whereas the magnetic moments of the pyridyl (1b: 2.4 B.M.) and pyrazyl (1c: 4.2 B.M.) substituents lead to spin transitions, the 6-picolyl (1d: 5.4 B.M.) substituent is a pure Curie paramagnet at 300 K. Interestingly, the Fe(II) complex of bromo-phenyl-2,2':6 '',2'-terpyridine (1a) displays significant anion effects in the solid state, with the ClO4 salt exhibiting major diamagnetic contributions (2.1 B.M. at 300 K) and the PF6 salt has more significant paramagnetic contributions (3.5 B.M. at 300 K). The Fe-N bond distances observed in the 6-picolyl complex [Fe(1d)(2)](ClO4)(2) for both the central rings 2.084 (5) angstrom and the distal rings 2.254 (4) and 2.369 (4) angstrom are significantly longer than those of the pyridyl complex [Fe(1b)(2)](ClO4)(2) (centre: 1.869 (4) angstrom; distal: 1.992 (4) angstrom; distal: 2.005 (4) angstrom) due to steric strain, thus generating high-spin [Fe(1d)(2)](ClO4)(2). (c) 2007 Elsevier Ltd. All rights reserved.