LAUSR

Abstract Mono and disubstituted tridentate Schiff base ligands were synthesized from the reaction of 2(2-aminoethyl)pyridine with 5-bromosalicylaldehyde (H-L1) and 3,5-dibromosalicylaldehyde (H-L2) respectively, which were subsequently reacted with NaBH4 to yield the corresponding reduced Schiff base ligands H-rL1 and H-rL2. The complexes; MnIII-(L1)2 (1), MnIII-(rL1)2 (3), and MnII-(L2)2 (2), MnII-(rL2)2 (4) were obtained by the reaction of the ligands with {Mn(ClO4)2·6H2O}. The ligands and complexes were characterized by UV–Vis, ESI-MS and FT-IR spectroscopy. The 1H NMR spectra of the ligands as well as the crystal structures, and electrochemical properties of the complexes were obtained. The crystal structures of MnIII-(L1)2 and MnII-(L2)2 show coordination of the ligands in tridentate mode in octahedral geometry. Cyclic voltammetric studies of Mn-(L1)2 and Mn-(L2)2 in acetonitrile solution show two prominent reversible peaks attributed to the redox processes: Mn(II)/Mn(III), (E1/2 = 0.203–(−0.204 V) and Mn(III)/Mn(IV), (E1/2 = 1.103–0.195 V) versus Ag/AgCl while that of Mn-(rL4)2 showed three quasi reversible peaks suggesting three redox couples: Mn(II)/Mn(III) (E1/2 = −0.109); Mn(III)/Mn(IV), (E1/2 = 0.125 and (Mn(IV)/Mn(V), (E1/2 = 0.649) vs Ag/AgCl. Epoxidation of cyclohexene and 1-hexene by hydrogen peroxide catalyzed by the manganese complexes gave epoxide yield of 42–53% with a turnover of 10.50–13.25 after 20 h of reaction for the reduced Schiff base complexes {MnIII-(rL1)2 and MnII-(rL2)2} at 0 °C.