Dynamics of molecules confined in nanocages. A deuteron NMR study at high temperature
Our published and new experimental results by means of deuteron NMR spectroscopy in studies of molecular mobility in confinement are summarized and annalysed. Conclusions about limits of applicability of methods in disclosing several features are achieved. A set of molecules: D2, CD4, D2O, ND3, CD3OD and (CD3)2CO was chosen and introduced into zeolites with faujasite structure. Measurements of deuteron spectra and relaxation in function of loading and temperature provide a wealth of cases. A tranistion from translational into rotational mobility on decreasing temperature was a common obsevation. Fast magnetization exchange between two subsystems with different mobility was considered as a model. Existence of D2O clusters and trimers of CD3OD was a particularly significant evidence for importance of mutual ineractions. Evolution of spectral components, derivation of the activation energy and T1/T2 ratio are among analysed features. Choice of the zeolite, eg. NaY or NaX, introduces specific inertactions with the zeolite framework. Temperature at wich molecules become immobilized on cage walls is related to the strength of the interactions. On increasing temperature we may observe features like for layers of liquid on cage walls and gaseus state. In general properly chosen molecules may be used for characterization of host microporous systems.