In a previous study of Sin et al., the co-adsorption of CO2 and CH4 in rigid and flexible crystals of DUT-8(Ni) was studied by C NMR. The residual anisotropy (i.e. the line width of the NMR signal) of the C NMR signal of C labelled CO2 can be directly related to the dynamic orientation of the CO2 molecules. Sin et al. found that the residual chemical shift anisotropy of CO2 is significantly smaller in the smaller, rigid crystals than in the larger, flexible crystals (see Figure ). The measured C signal is for both rigid and flexible crystals much broader than in gaseous CO2 (the gas peak is observed at approx. 126 ppm, see Figure ), some dynamic order therefore remains even in the smallest crystals measured. This observation could back then not be attributed to a single cause, but two possible reasons were suggested: First, the smaller anisotropy could be caused by faster inter-particle exchange. Or second, the flexible framework could apply an ordering force onto the adsorbed CO2 molecules that is not present in the rigid framework.