FORMATION OF CU-I-N-2 ADDUCTS AT 298 AND 77 K IN CU-I-ZSM-5 - AN FTIR INVESTIGATION

Cu-I-exchanged ZSM-5 contacted with N-2 at room temperature or at 77 K exhibits a narrow IR band at 2295 cm(-1). On the basis of N-14(2)/N-14(2) and N-14(2)/(NN)-N-14-N-15/N-15(2) isotopic substitution experiments this peak is assigned to the N-N stretching vibration of Cu-I-N-2 end-on dinitrogen complexes formed on isolated Cu-I sites inside the zeolite channels. The problem of the location of the Cu-I ions and the role of surface heterogeneity in determining the FWHM (ca. 9 cm(-1) at N-2 coverage theta=1) of the 2295 cm(-1) band are discussed. Some hypotheses concerning the bonding structure are made by comparison with the spectra of the purely electrostatic M(+)-N-2 and M(+)-CO adducts (where M(+) is an alkali-metal ion) and of the Cu-I-CO complex formed on the same support.