Accessibility of Manganese Oxidation States. Control by Pentaaza Macrocyclic Ligands

The synthesis and characterization of a series of manganese(II) and -(III) and zinc(II) complexes with 15-17-membered pentaaza and 14-membered tetraaza macrocyclic ligands are reported. Except for two of the complexes with the largest ring, [17]pydieneN₅, all of the divalent compounds incorporating the pentadentate ligands appear to exhibit pentagonal-type coordination geometry in the solid state. Solution infrared and NMR studies (¹H and ¹³C) on the diamagnetic Zn(II) complexes indicate that in solution all of the pentadentate ligands display a pentagonal coordination geometry. The Mn(II) complexes with the 15-membered pentadentate ligand can be oxidized by NOPF₆ to stable Mn(III) products. The pentagonal-bipyramidal coordination geometry displayed by the new complexes is highly unusual and has not been previously observed for Mn(III). These high-spin d⁴ complexes are deeply colored and exhibit d-d spectra which have been interpreted using a simple one-electron model. The accessibility of the trivalent oxidation state as a function of ligand structure is discuss.