Oxygen-17 NMR spectroscopy of water molecules in solid hydrates

O-17 solid-state NMR studies of waters of hydration in crystalline solids are presented. The O-17 quadrupolar coupling and chemical shift (CS) tensors, and their relative orientations, are measured experimentally at room temperature for alpha-oxalic acid dihydrate, barium chlorate monohydrate, lithium sulfate monohydrate, potassium oxalate monohydrate, and sodium perchlorate monohydrate. The O-17 quadrupolar coupling constants (C-Q) range from 6.6 to 7.35 MHz and the isotropic chemical shifts range from -17 to 19.7 ppm. The oxygen CS tensor spans vary from 25 to 78 ppm. These represent the first complete CS and electric field gradient tensor measurements for water coordinated to metals in the solid state. Gauge-including projector-augmented wave density functional theory calculations overestimate the values of C-Q, likely due to librational dynamics of the water molecules. Computed CS tensors only qualitatively match the experimental data. The lack of strong correlations between the experimental and computed data, and between these data and any single structural feature, is attributed to motion of the water molecules and to the relatively small overall range in the NMR parameters relative to their measurement precision. Nevertheless, the isotropic chemical shift, quadrupolar coupling constant, and CS tensor span clearly differentiate between the samples studied and establish a 'fingerprint' O-17 spectral region for water coordinated to metals in solids.