Manganese(III) complexes with asymmetrical ONSN tetradentate Schiff bases have been prepared. Ligands are derived from the iminic condensation of substituted salicylaldehydes and 4-[(2′-amino-ethyl)thiomethyl]-5-methylimidazole (H 2 MIS–X) or2-[(2-aminoethyl)thiomethyl]-benzimidazole (H 2 BIS–X). Physicochemical data (mean)indicate that ligands act as tetradentate mono- or dianionic, in di- and mono-cationic complexes, respectively.[Mn(MIS–X)(H 2 O)]ClO 4 · nH 2 O, [Mn(BIS–X)(H 2 O)]ClO 4 and [Mn(HMIS–X) (H 2 O)](ClO 4 ) 2 · nH 2 O (n=0, 2, 4) have been characterized by elemental analyses, Λ M ,IR, UV–VIS and mass spectrometries, magnetic measurements at room temperature and cyclicvoltammetry, being their low solubility a handicap. These data, point to an octahedral geometry around the metal with, at least, a dimeric array through the phenolic oxygen atoms.