MONO-BRIDGED AND DI-BRIDGED MU-OXO DIIRON COMPLEXES OF 3-[BIS(2-PYRIDYLMETHYL)AMINO]PROPIONATE (BPP) - CRYSTAL-STRUCTURES OF [(FE(BPP)(H2O)CENTER-DOT-2O][CLO4]2-CENTER-DOT-H2O AND [(FE(BPP)CENTER-DOT-2(MECO2)O][CLO4]CENTER-DOT-4.5H2O

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 mu-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 P1BAR, with a = 13.260(4), b = 14.389(4), c = 11.347(3) angstrom, alpha = 92.224(14), beta = 113.722(13), gamma = 97.719(17)degrees 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 mu-oxo group with average Fe-O 1.790(4) angstrom, Fe-O-Fe 168.8(3)degrees and Fe ... Fe 3.564(2) angstrom. 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. Mu-oxo complexes containing supporting mu-acetato and mu-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]-4.5HO 2, has been carried out and shows that the iron atoms are doubly-bridged by a mu-oxide atom and mu-acetato group, with average Fe-O 1.82(2) angstrom, Fe-O-Fe 129(1)degrees and Fe ... Fe 3.245(6) angstrom. 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.