A Study of the Composition, Ionic and Molecular Mobility, and Thermal Properties of Ammonium Pentafluoridozirconate Hydrates

Abstract

The effect of hydrate number on the structural changes, thermal properties, and ionic (molecular) mobility character in NH₄ZrF₅ ⋅ H₂O, NH₄ZrF₅ ⋅ 0.75H₂O crystal hydrates have been investigated by the methods of IR, Raman, nuclear magnetic resonance (NMR) (¹H, ¹⁹F, including ¹⁹F MAS), and TG-DTA spectroscopy. Differences in crystal hydrate structures—anion structure, molecular state of water, and O–H⋅⋅⋅F, N–H⋅⋅⋅F hydrogen bond strengths—have been corroborated by IR and Raman spectroscopy data. Isotropic chemical shifts of magnetic inequivalent positions have been determined and attributed to crystal structures of the studied compounds by the method of ¹⁹F MAS NMR. It has been established that the removal of water molecules from NH₄ZrF₅ ⋅ H₂O and NH₄ZrF₅ ⋅ 0.75H₂O results in the transformation of chain or layered structures accompanied by the increase of the number of bridge bonds while retaining or increasing the dimensionality of the anion structural motif. According to the ¹H NMR data, the NH\(_{4}^{ + }\) cation diffusion in NH₄ZrF₅ occurs only in the temperature range of 370–520 K.