High-resolution solid-state magic angle spinning nuclear magnetic resonance studies on the layered antimony hydrogen phosphate, HSb(PO₄)₂·2H₂O, and its reaction products with tetrakis(pyridyl)iron(II) chloride

Abstract

The antimony hydrogen phosphate, HSb(PO₄)₂ ·2H₂O (denoted H₁SbP₂ ·2H₂O), has been synthesised via the ion exchange of crystalline KSb(PO₄)₂ , (K₁SbP₂), with 9 m HNO₃ . Scanning electron microscopy (SEM) confirmed that the crystalline K₁SbP₂ was formed by the so-called ‘deck of cards’ mechanism to give randomly orientated lamellae. The synthesised H₁SbP₂ ·2H₂O host material was studied using ¹H and ³¹P magic angle spinning nuclear magnetic resonance (MAS NMR) techniques. Intercalation studies were carried out using tetrakis(pyridyl)iron(ii) chloride, [Fe(py)₄Cl₂ ]·H₂O. The resulting products were analysed using powder X-ray diffraction (PXRD) and ³¹P MAS NMR techniques. The former suggested that the [Fe(py)₄Cl₂ ]·H₂O complex lost its water of crystallisation during the reaction and did not intercalate in its intact state between adjacent layers of the H₁SbP₂ ·2H₂O crystallites. ³¹P MAS NMR data suggested that the H₁SbP₂ ·2H₂O–[Fe(py)₄Cl₂ ] reaction products contained phosphorus resonances which could be assigned as belonging to (i) unaltered host H₁SbP₂ ·2H₂O (protonated) phosphate groups, (ii) phosphate groups bonded to the intercalating species. In addition, a separate, Q_P³ , resonance was also noted which was thought to arise from a chemically unaltered phosphate group of the host H₁SbP₂ ·2H₂O perturbed by the close proximity of the sorbed [Fe(py)₄ ]²⁺ cationic species.

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