IRON(II) COMPLEXES OF POLYDENTATE AMINOPYRIDYL LIGANDS AND AN EXCHANGEABLE 6TH LIGAND REACTIONS WITH PEROXIDES - CRYSTAL-STRUCTURE OF [FEL(1)(H2O)][PF6](2)CENTER-DOT-H2O [L(1)=N,N'-BIS(6-METHYL-2-PYRIDYLMETHYL)-N,N'-BIS(2-PYRIDYLMETHYL)ETHANE-1,2-DIAMINE]

Iron(II) complexes of the pentadentate ligand N-methyl-N,N',N'-tris(2-pyridylmethyl)ethane-1,2-diamine (L(2)) and the potentially hexadentate ligand N,N'-bis(6-methyl-2-pyridylmethyl)-N,N'-bis(2-pyridylmethyl)ethane-1,2-diamine (L(1)) have been isolated. Both ligands behave as pentadentate ligands in their iron(II) complexes with the general formulation [FeL(X)](n+) (L = L(1) or L(2), n = 1 or 2) with the sixth co-ordination site (X) occupied by an auxiliary ligand e.g. H2O, Cl, SCN or CN. The crystal structure of [FeL(1)(H2O)][PF6](2) . H2O 1 shows that the nitrogen atom of one of the 6-methyl-2-pyridylmethyl groups of the formally hexadentate ligand is not co-ordinated to the iron atom. Instead a water molecule occupies the sixth co-ordination position. Complex 1 crystallizes in the triclinic space group P (1) over bar, with a = 10.485(2), b = 13.161(5), c = 14.853(6) Angstrom, alpha = 69.31(4), beta = 74.42(3), gamma = 66.37(3)degrees and Z = 2. The structure refined to a final R value of 0.052 for 2531 reflections. The complexes show peroxidase activity, the availability of a labile site on the relatively stable iron(II) complexes. along with no apparent tendency to form oxo-bridged diiron(III) species, which are likely to be crucial factors in the mechanism of the oxidation reactions. Efforts to isolate a complex with a co-ordinated peroxide in the sixth position were unsuccessful. However. we have spectroscopic evidence that peroxide reacts with the iron(II) complexes to form an unstable species, probably of the form [Fe(III)L(OOR)](2+) (L = L(1) or L(2), R = H or Bu(t)). The peroxide ligand in this iron(III) complex is likely to be forced into an 'end-on' co-ordination mode.