Formation of CuI—N2 adducts at 298 and 77 K in CuI-ZSM-5: an FTIR investigation

CuI-exchanged ZSM-5 contacted with N2 at room temperature or at 77 K exhibits a narrow IR band at 2295 cm–1. On the basis of 14N2/14N2 and 14N2/14N15N/15N2 isotopic substitution experiments this peak is assigned to the N—N stretching vibration of CuI—N2 end-on dinitrogen complexes formed on isolated CuI sites inside the zeolite channels. The problem of the location of the CuI ions and the role of surface heterogeneity in determining the FWHM (ca. 9 cm–1 at N2 coverage = 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+–N2 and M+–CO adducts (where M+ is an alkali-metal ion) and of the CuI—CO complex formed on the same support.