Room temperature solid surface water with tetrahedral jumps of 2H nuclei detected in 2H2O-hydrated porous silicates

The nature of water adjacent to solid silicate surfaces in kanemite, rehydrated zeolite A, rehydrated highly porous glass, rehydrated high surface area silica get, and the hydration products of tricalcium silicate has been investigated with H-2 NMR techniques and calorimetry. The room temperature H-2 NMR quadrupole echo spectra of all samples show a sharp central resonance that corresponds to (H2O)-H-2. The kanemite, porous glass, and silica gel spectra show in addition powder patterns that were assigned, based on previous findings for kanemite, to silanol -OH groups experiencing rapid 3-fold jumps or rotational diffusion about the Si-O bond. The spectrum of hydrated tricalcium silicate shows in addition to the aqueous peak a rigid powder pattern that is assigned to Ca((OH)-H-2)(2). Spectra obtained at - 120 and - 150 degreesC for the kanemite sample show that the qcc values for the aqueous deuterons range from 180 to 210 kHz, as would be expected for the different water environments observed in the X-ray structure of kanemite. Room temperature H-2 T-1 data obtained at two magnetic fields for kanemite are exactly matched with theoretical calculations that assume rapid tetrahedral jumps of the H-2 nuclei (2.0 x 10(8) s(-1)) in a solid-state lattice similar to those observed in (H2O)-H-2 ice below the freezing point. The T-1 data cannot be matched with isotropic rotational diffusion as would be expected for liquid water. The T-1 data for low loadings of (H2O)-H-2 in zeolite A are also matched with the tetrahedral jump model. T-1 data for the other samples are consistent with rapid exchange of H-2 nuclei or (H2O)-H-2 molecules between solid-state surface water experiencing rapid tetrahedral jumps and liquid-state water farther front the surface. Heat evolution observed during hydration of all samples is consistent with the heat of fusion expected for a liquid to solid phase transition for the surface water.