Synthesis and characterization of Cu(I)–salen complex immobilized aluminosilicate MCM-41

Copper(I)–salen: N,N−-ethylenebis(salicylidene-iminato)copper(I), immobilized into the structure of Al-MCM-41 has been synthesized by a liquid-phase adsorption of salen through Cu(I)-exchanged Al-MCM-41 (Cu(I)–salen/Mimp) and by a flexible ligand method (Cu(I)–salen/Mss). The ligand and complex were characterized by various physico-chemical measurements such as elemental analysis, powder XRD, mid-spectral FT-IR, thermal analysis (TGA, DTGA), surface texture and scanning electron microscopy (SEM). A comparative in situ FT-IR study of CO adsorption onto simple Cu(I)-exchanged Al-MCM-41 and the complex-immobilized Al-MCM-41 has been carried out. The structure of Al-MCM-41 after modification remains intact, which was evident from XRD and FT-IR studies. The surface characteristics and thermal analysis have provided evidence for successful immobilization of the copper complex inside Al-MCM-41. The structure of Cu(I)–salen complex in Al-MCM-41 prepared by the liquid-phase adsorption of salen was more thermally stable than the analogous prepared by the flexible ligand method. The in situ FT-IR investigation of CO adsorption showed a band at 2124 cm−1 due to Cu(I)–CO in the spectrum of Cu(I)-exchanged Al-MCM-41. This band was shifted to 2146 cm−1 in the spectra of Al-MCM-41-containing complex due to a stronger mode of CO interaction. The Cu(I)–salen/Mimp sample was more active than the Cu(I)–salen/Mss one in the generation of CO2 (2336 cm−1), which was produced from CO and H2O by the water–gas shift reaction. Surface bound adsorbed species like carbonate (1636, 1590, 1488 and 1434 cm−1) and formate (1727 cm−1) were also detected. The spectrum of the Cu(I)–salen/Mss sample was characterized by a band at 2278 cm−1 assigned to isocyanate ion, NCO−, coordinated to a Cu(I) ion which was absent in the spectra of other samples. The extent of this band depends on the interaction of the immobilized complex with the Al-MCM-41 lattice.