Surprising Coordination Chemistry Of Cu+ Cations In Zeolites: Ftir Study Of Adsorption And Coadsorption Of Co, No, N-2, And H2o On Cu-Zsm-5

Cations exchanged in zeolites are generally characterized by a low coordination number and can thus attach simultaneously more than one small guest molecule. For instance, Cu+ ions in ZSM-5 can accept, at low temperature, up to three CO and up to two NO molecules. However, only one N-2 molecule can be coordinated to such sites. Although mixed aqua-carbonyl and aqua-dinitrogen complexes are formed, no mixed carbonyl-nitrosyl, carbonyl-dinitrogen, or nitrosyl-dinitrogen species can be produced. Thus, adsorption of NO on CO precovered sample results in segregation of the CO adsorption layer according to the reaction: 2Cu(+)-CO + 2NO -> Cu+(CO)(2) + Cu+(NO)(2). Adsorption of N-2 on NO precovered sample leads to a similar process: 2Cu(+)-NO + N-2 -> Cu+(NO)(2) + Cu+-N-2. No carbonyl-dinitrogen complexes are produced during CO-N-2 coadsorption. The role of the ligand and the nature of the bond in the formation of geminal and mixed-ligand complexes are discussed.