Redox properties of bis(8-hydroxyquinoline)manganese(II) encapsulated in various zeolites

Abstract

Bis(8-hydroxyquinoline)manganese(II) [Mn(C9 H6 NO)2 (Mn–Qn)] was encapsulated in NaY, KL, MCM-41, Na and Na-ZSM-5. Charac-terization of the catalysts was done by using IR, UV–vis and EPR spectroscopy whereas redox properties of neat and encapsulated Mn–Qn complexes were evaluated by cyclic voltammetry. Peak broadening and different electrochemical responses are observed upon encapsulation of Mn–Qn complex in various zeolites, thus indicating that Mn–Qn complexes have altered values of redox potential in various positions of zeolite. In order to compare biological systems with metal complexes encapsulated in various zeolites, cytochrome-c was immobilized in MCM-41. Redox potential of cytochrome-c is shifted towards more positive value upon immobilization in MCM-41. This has been attributed to be due to conformational change of cytochrome-c in MCM-41. Change of redox potential of Mn–Qn complex in zeolites is due to change in the positions of HOMO and LUMO levels of metal complexes. Density functional theory (DFT) is employed to calculate the position of HOMO and LUMO levels of metal complexes in zeolite cluster models. The catalytic activity towards oxidation of cyclohexanol was performed using neat and encapsulated Mn–Qn complexes. Encapsulated complexes shows higher activity compared to that of neat complex.