High-Resolution ¹⁷O NMR Spectroscopy of Structural Water

The importance of studying site-specific interactions of structurally similar water molecules in complex systems is well known. We demonstrate the ability to resolve four distinct bound water environments within the crystal structure of lanthanum magnesium nitrate hydrate via ¹⁷O solid state nuclear magnetic resonance (NMR) spectroscopy. Using high-resolution multidimensional experiments at high magnetic fields (18.8–35.2 T), each individual water environment was resolved. The quadrupole coupling constants and asymmetry parameters of the ¹⁷O of each water were determined to be between 6.6 and 7.1 MHz, 0.83 and 0.90, respectively. The resolution of the four unique, yet similar, structural waters within a hydrated crystal via ¹⁷O NMR spectroscopy demonstrates the ability to decipher the unique electronic environment of structural water within a single hydrated crystal structure.