Unexpected structural/motional mode of water intercalated into an α-crystalline zirconium phosphate deduced by 31 P and 2 H solid-state MAS NMR spectra

Abstract

In developing the approach to understanding dynamics of intercalates in layered materials, crystalline-layered zirconium phosphate Zr (HPO₄ )₂ ·0.35D₂ O has been prepared and characterized by the ¹ H, ³¹ P, and ² H solid-state MAS NMR spectra, including ³¹ P and ² H T₁ measurements. At temperatures >253 K, the intercalated water shows two spectrally-distinguished deuterons unprecedentedly with different DQCC's and ² H T₁ times, one of which is hydrogen bonded. The collected data allowed to identify an unexpected bonding/dynamic mode of water molecules, which experience fast rotation around the hydrogen bond, formed with a zirconium-coordinated oxygen. The low-temperature ² H MAS NMR experiments have demonstrated the presence of additional hydrogen bond P(H)O˙˙˙ DO, population of which grows on cooling to 195 K corresponding to the doubly hydrogen-bonded immobile water molecule.

Keywords: NMR; dynamics; relaxation; structural elucidation; zirconium phosphates.