Mono- and di-bridged µ-oxo diiron complexes of 3-[bis(2-pyridylmethyl)amino]propionate (bpp). Crystal structures of [{Fe(bpp)(H2O)}2O][ClO4]2·H2O and [{Fe(bpp)}2(MeCO2)O][ClO4]·4.5H2O
Abstract
Oxo-bridged dinuclear iron(III) complexes of the new tetradentate ligand, the conjugate base of 3-[bis(2-pyridylmethyl)amino]propionic acid (Hbpp), have been prepared. The structure of the monobridged µ-oxo-diiron(III) complex [{Fe(bpp)(H2O)}2O][ClO4]2·H2O 1 shows that the bpp is co-ordinated to each iron centre as a terminal capping ligand. A water molecule completes the co-ordination sphere of each iron atom. Complex 1 crystallizes in the triclinic space group P, with a= 13.260(4), b= 14.389(4), c= 11.347(3)Å, α= 92.224(14), β= 113.722(13), γ= 97.719(17)° and Z= 2. The structure refined to a final R value of 0.077 for 4249 reflections. The Fe atoms are bridged by a single µ-oxo group with average Fe–O 1.790(4)Å, Fe–O–Fe 168.8(3)° and Fe ⋯ Fe 3.564(2)Å. The cations are linked by hydrogen bonds forming chains parallel to the b axis. The co-ordinated water molecules of 1 can be replaced easily by the two co-ordinating atoms of bidentate oxo anions to form dibridged complexes. µ-Oxo complexes containing supporting µ-acetato and µ-phosphato bridges were prepared in this fashion. These substitution reactions involve a contraction of the Fe–O–Fe angle. A structural characterization of the acetato-bridged complex, [{Fe(bpp)}2(MeCO2)O][ClO4]·4.5H2O 2, has been carried out and shows that the iron atoms are doubly-bridged by a µ-oxide atom and µ-acetato group, with average Fe–O 1.82(2)Å, Fe–O–Fe 129(1)° and Fe ⋯ Fe 3.245(6)Å. Complexes 1 and 2 show strong antiferromagnetic coupling, as is usually observed in oxo-bridged iron pairs; J=-114 and -110 cm–1 for 1 and 2 respectively.