Iron(II) complexes of polydentate aminopyridyl ligands and an exchangeable sixth ligand; reactions with peroxides. Crystal structure of [FeL1(H2O)][PF6]2·H2O [L1=N,N′-bis-(6-methyl-2-pyridylmethyl)-N,N′-bis(2-pyridylmethyl)ethane-1,2-diamine]