Combined X-ray and neutron powder refinement and NMR study of hydrochlorofluorocarbon HCFC-124a (CF2HCF2Cl) binding on NaX

The structure of hydrochlorofluorocarbon (HCFC) 124a (CF2HCF2Cl) adsorbed on NaX has been determined at 100 K. by performing simultaneous Rietveld analyses of both X-ray and neutron data. The HCFC molecule is localized above the four rings, and is bound via fluorine atoms on both the CF2H and CF2Cl groups to sodium cations in the SII and SIII' positions. Both this model and the H-1 MAS NMR are consistent with hydrogen bonding between the proton of the HCFC and the framework oxygen. Cations were found at the SI', SII, and SIII' positions, after gas sorption. The positions and occupancies do not differ significantly from those previously reported in the low-temperature structures of NaX, Na-23 MAS NMR demonstrates that the SIII cations in the supercages are mobile at room temperature in the bare zeolite, but that lowering the temperature or gas sorption lock's these cations in place. Variable offset F-19 to Na-23 cross polarization (CP) MAS NMR spectroscopy was used to probe fluorocarbon-cation proximity. More efficient CP was observed from the fluorine atoms on the CF2H group, in comparison to the CF2Cl fluorine atoms. This was ascribed to the larger number of cations coordinated to this group. This is consistent with the model obtained from the diffraction studies. where the CF2H group is bound to two cations, while the CF2Cl group is bound to only one cation.