The dual role of Para-phenyl substituents in aromatic imine ligand complexes of manganese and chromium

The voltammetric behavior of the bis complexes of manganese(II) and chromium(III) with the ligand 2,6-bis(4-phenyl-2-pyridyl)-4-phenyl-pyrdine (terosite) has been studied in acetonitrile using DC and AC polarography and cyclic voltammetry. The manganese(II) complex undergoes two one-electron reductions to the +1 and zero formal oxidation states, respectively, and a poorly defined one-electron oxidation to the +3 formal oxidation state. The bis(terosite)chromium(III) complex shows four one-electron reductions to the +2, +2, 0, and −1 formal oxidation states, respectively. Comparison of half-wave potentials is made on the corresponding complexes of manganese and chromium with the ligands: 2,6-bis-(2pyridyl)pyridine(terpyridine)and 2,6-bis(2-pyridyl)-4-phenylpyridine (terosine). Redox potentials and comparisons of behaviour are also presented for the cobalt and iron complexes with the three ligands mentioned above. All comparisons indicate that the para phenyl substituent is able to stabilize both the high and low formal oxidation states of the complexes. Spectroscopic and magnetic data are also given.