Manganese(III) complexes containing optically active tetradentate Schiff Base ligands have been prepared. The crystal structure of the complex [Mn{7-Phsal-(SS)-stien}Cl]. CH2Cl2, where 7-Phsal-(SS)-stien is the dianion of the product formed from the condensation of 2 mol of 2-hydroxybenzophenone and 1 mol of (S,S)-1,2-diphenylethylenediamine, has been established by the X-ray method. Crystal data : monoclinic, P2(1), a = 16.796(2) Angstrom, b = 14.366(2) Angstrom, c = 15.266(2) Angstrom, beta = 101.84(1)degrees, V = 3605.2(9) Angstrom 3, Z = 4. The structure was refined to R = 0.058 and R(w) = 0.063. The coordination polyhedron is a distorted square pyramid, the Schiff base ligand occupying the basal sites and the chloride the apical site. The two phenyl groups of the diamine moiety are in the axial positions, and the central chelate ring of the Schiff base ligand assumes a lambda gauche conformation. On the basis of the circular dichroism spectral data for [Mn{7-Phsal-(SS)-stien}Cl] and related complexes, the preferred conformation of the central chelate ring in solution is assigned. The effects of phenyl substituents on the Mn(III)/Mn(II) and Mn(IV)/Mn(III) redox potentials are discussed in terms of the conformational behavior of the Schiff base ligands. The manganese(III) complexes with axial phenyl groups offer great opposition to oxidation.