Solid state water motions revealed by deuterium relaxation in 2H2O-synthesized kanemite and 2H2O-hydrated Na+-Zeolite A

Deuterium NMR relaxation experiments, low temperature deuterium NMR lineshape analysis, and FTIR spectra are consistent with a new model for solid state jump dynamics of water in 2H2O-synthesized kanemite and 2H2O-hydrated Na+-Zeolite A. Exchange occurs between two populations of water: one in which water molecules are directly coordinated to sodium ions and experience C2 symmetry jumps of their OH bonds, and a population of interstitial water molecules outside the sodium ion coordination sphere that experience tetrahedral jumps of their OH bonds. For both samples the C2 jump rate is much faster than the tetrahedral jump rate. 2H NMR relaxation experiments match well with the fast exchange regime of the model over a wide range of temperatures, including room temperature and above. For hydrated Zeolite A, the kinetic activation parameters for the tetrahedral and C2 symmetry jumps are ΔHtet‡ = +17 kJ/mol, ΔStet‡ = −109 J/(mol K), ΔHC2‡=+19kJ/mol, and ΔSC2‡=-20J/(mol K). For kanemite, ΔHtet‡ = +23 kJ/mol, ΔStet‡ = −69 J/(mol K),ΔHC2‡=+23kJ/mol, and ΔSC2‡=-11J/(mol K).