Syntheses and characterisation of mono- and di-nuclear iron(III) complexes of 1,4,7-triazacyclononane-N-acetate (L). Crystal structures of [FeCl2L] and [Fe2(µ-O)(µ-O2CMe)L2]ClO 4· NaClO4·2H2O

Abstract

The macrocycle 1,4,7-triazacyclononane-N-acetate (L) reacted with FeCl ₃ ·6H ₂ O in water to form the monomeric complex [FeCl ₂ L] 1. Hydrolysis of 1 in the presence of an excess of sodium acetate and sodium perchlorate yielded the binuclear complex [Fe ₂ (µ-O)(µ-O ₂ CMe)L ₂ ]ClO ₄ ·NaClO ₄ ·2H ₂ O 2. Complexes 1 and 2 have been characterised by X-ray crystallography. In 1 the Fe ^III is surrounded by a distorted-octahedral array of one fac-co-ordinated triamine ring, one monodentate carboxylato group and two chloride ligands. Complex 2 consists of a µ-oxo-µ-acetato-diiron(III) core with the distorted octahedral co-ordination sphere about each Fe ^III being completed by the ligand L. A sodium ion, with distorted trigonal-bipyramidal stereochemistry, bridges between the co-ordinating carboxylate oxygens of the terminal ligands. Complex 2 exhibits spectroscopic features and magnetic properties similar to those of other µ-oxo-diiron(III) complexes as well as metalloproteins incorporating a µ-oxo-diiron(III) unit at their active sites.