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 Δ H_tet^‡ = +17 kJ/mol, Δ S_tet^‡ = -109 J/(mol K), Δ H_C2^‡ = + 19 kJ / mol, and Δ S_C2^‡ = - 20 J / (mol K). For kanemite, Δ H_tet^‡ = +23 kJ/mol, Δ S_tet^‡ = -69 J/(mol K),Δ H_C2^‡ = + 23 kJ/mol, and Δ S_C2^‡ = - 11 J / (mol K).