Chemistry of polydentate ligands. Part 8. Preparation and properties of iron(II) complexes with quinquedentate macrocyclic ligands. Crystal and molecular structure of a compound where high-spin Fe^II sits in the ligand cavity. Electrochemistry of a series of complexes with the macrocycles

Complexes of quinquedentate macrocyclic ligands with Fe^II have been prepared by condensation of 2,6-diacetylpyridine and 2,6-diformylpyridine with 2,9-di(1-methylhydrazino)-1,10-phenanthroline monohydrochloride in the presence of iron(II) templates. Magnetic susceptibility measurements and Mössbauer parameters show that the complexes are high spin, while chemical evidence indicates that the macrocycles encompass iron(II). This is confirmed by a structure determination on a single crystal of [FeC₂₃H₂₅N₇O₂][B₂F ₈], which is monoclinic with a = 14.152(3), b = 11.464(11), c = 16.732(5) Å, β = 93.56(3)°, Z = 4, space group P2₁/c. Metal-donor nitrogen distances are 2.100(9), 2.112(8), 2.116(7), 2.242(8), and 2.276(8) Å. The co-ordination geometry of the iron(II) is pentagonal bipyramidal with water molecules occupying the axial sites: Fe-O distances are 2.213(7) and 2.194(7) Å. This structure is compared with those of high-spin iron(II) complexes of other macrocycles. Cyclic voltammetry data for selected complexes of Mn^II, Fe^II, Zn^II, and Cd^II with the ligands are presented: one-electron reductions produce π-anion radicals.