Unique tetranuclear copper(II) cluster and monomeric iron(II), (III) complexes with a tris(imidazolyl) chelating ligand

Copper(II) and iron(II, III) complexes of the tripodal ligand, tris(1-methyl-1H-imidazol-2-yl)methanol (Htmim), have been synthesized and characterized by elemental analysis, H-1 NMR and IR spectroscopies, magnetic moment measurement and X-ray crystallography. The structure of the copper complex, [Cu-4(tmim)(4)(CF3SO3)(2)](CF3SO3)(2). 2MeOH (1), can be regarded as a polyimidazole-linked tetranuclear cluster where each copper atom adopts a five-coordinate square-pyramidal geometry ligated by the tmim anion. The two iron complexes, [Fe-II(Htmim)(2)][(FeCl4)-Cl-II]. 4MeOH (2) and [Fe-III(Htmim)(2)][(FeCl4)-Cl-III](2)Cl (3), contain the isostructural [Fe(Htmim)(2)] cation and tetrahedral [FeCl4](-) anion. While Htmim shows a normal tripodal tridentate mode in the iron complexes capping one face of an essentially octahedral coordination sphere, its deprotonated species exhibit an unusual non-tripodal tetradentate coordination with copper(II) ions. The observed magnetic moment at room temperature for 1 is 1.13 BM per Cu atom, consistent with antiferromagnetic coupling between the copper(II) atoms of the tetramer. Both 2 and 3 show magnetic properties consistent with low-spin electronic configurations of the cation and high-spin nature of the metal ion in the anion. (C) 1999 Elsevier Science Ltd. All rights reserved.