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(PO ₄ ) ₂ ·2H ₂ O (denoted H ₁ SbP ₂ ·2H ₂ O), has been synthesised via the ion exchange of crystalline KSb(PO ₄ ) ₂ , (K ₁ SbP ₂ ), with 9 m HNO ₃ . Scanning electron microscopy (SEM) confirmed that the crystalline K ₁ SbP ₂ was formed by the so-called ‘deck of cards’ mechanism to give randomly orientated lamellae. The synthesised H ₁ SbP ₂ ·2H ₂ O host material was studied using ¹ H and ³¹ P magic angle spinning nuclear magnetic resonance (MAS NMR) techniques. Intercalation studies were carried out using tetrakis(pyridyl)iron(ii) chloride, [Fe(py) ₄ Cl ₂ ]·H ₂ O. The resulting products were analysed using powder X-ray diffraction (PXRD) and ³¹ P MAS NMR techniques. The former suggested that the [Fe(py) ₄ Cl ₂ ]·H ₂ O complex lost its water of crystallisation during the reaction and did not intercalate in its intact state between adjacent layers of the H ₁ SbP ₂ ·2H ₂ O crystallites. ³¹ P MAS NMR data suggested that the H ₁ SbP ₂ ·2H ₂ O–[Fe(py) ₄ Cl ₂ ] reaction products contained phosphorus resonances which could be assigned as belonging to (i) unaltered host H ₁ SbP ₂ ·2H ₂ O (protonated) phosphate groups, (ii) phosphate groups bonded to the intercalating species. In addition, a separate, Q _P ³ , resonance was also noted which was thought to arise from a chemically unaltered phosphate group of the host H ₁ SbP ₂ ·2H ₂ O perturbed by the close proximity of the sorbed [Fe(py) ₄ ] ²⁺ cationic species.