Solid-state NMR studies of novel porous solids: Structure and dynamics

Solid-state NMR is ideally suited to characterise solids lacking long-range periodicity such as molecular sieves, glasses, inorganic/organic hybrids, polymers and solid proteins. Recent advances in solid-state NMR spectroscopy have made it possible not only to elucidate the structure of such solids but also to characterise their dynamics. Rapid developments in instrumentation and pulse-programming methodology resulted in the measurements of the solid-state NMR spectra with the resolution comparable to that in solution-state NMR as well as the extraction of the unique structural and dynamic information on the basis of different anisotropic magnetic interactions as the latter can be reintroduced under the Magic-Angle Spinning (MAS) to measure distances or establish correlations based on proximity. We have used various double-resonance and two-dimensional solid-state NMR methods (e.g. cross-polarisation (CP), CP dynamics, 2D Wide-line correlation spectroscopy (WISE), Heteronuclear correlation spectroscopy (HETCOR)) to study novel porous solids with different structures and chemical compositions e.g. mesoporous molecular sieves, surfactant containing mesostructured solids, supported porous catalysts, and periodic mesoporous organosilicas. The synthesis pathway to these materials is based on the complex supramolecular and colloidal interactions of the inorganic precursors with surfactant micellar templates leading to complex functional materials with low structural ordering but relatively well-arranged system of uniform pores. Main focus of these studies was to identify structural and dynamic heterogeneities in the complex multi-component solids, and to gain a better insight into the understanding of the structure of the inorganic/organic interface through investigating the intermolecular interactions responsible for a particular overall structural arrangement. Several novel solid-state NMR techniques, which can be used for elucidation of the domain sizes in the complex solids, for measurements of distances and studying intermolecular interactions in supramolecular solids, are also being reviewed.