A comparative study of high-spin manganese and iron complexes

Different metal complexes of the general form M(OH)(n)(H2O)(6-n) have been studied for manganese and iron, Oxidation states considered for manganese are Mn(III). Mn(IV) and Mn(V) and for iron Fe(II). Fe(III) and Fe(IV), Oxygen containing ligands are used throughout with varying numbers of hydroxyl and water ligands. Some metal-ore and some charged complexes were also studied. Large Jahn-Teller distortions were found for the Mn(III) and Fe(IV) complexes. Consequences of these distortions are that water ligands have to be placed along the weak JT-axis and that five-coordination by a loss of one of these water ligands is quite competitive with six-coordination in particular for manganese. For Fe(II) and Fe(III) lower coordinations than six are preferred due to the presence of two repulsive e(g) electrons, For the metal-ore complexes five-coordination is also preferred due to the strong trans effect from the oxo ligand. All complexes studied have high-spin ground states, An interesting: effect is that the spill is much more delocalized on the ligands for the iron complexes than for the manganese complexes, This effect, which is chemically important for certain iron enzymes, is rationalized by the large number of 3d electrons oil iron, For manganese with only five 3d electrons no spill delocalization is needed to obtain the proper high-spin states.