Novel aluminium phenyl, benzyl, and bromobenzylphosphonates: structural characterisation and hydration–dehydration reactions

Reaction of phosphonic acids RPO(OH)₂ (R = phenyl, benzyl, 4-bromobenzyl) with aluminium nitrate and sulfate under various hydrothermal conditions led to three novel aluminium phosphonates, Al(OH)(O₃PCH₂C₆H₄Br)·H₂O, Al(OH)(O₃PCH₂C₆H₅)·H₂O and Al₂(O₃PC₆H₅)₃·H₂O. All the compounds were characterised by powder XRD, elemental analysis, TGA, ²⁷Al and ³¹P MAS NMR and IR spectroscopy. The same tools were used to study the dehydration–rehydration reactions. Refinement of the structure of Al(OH)(O₃PCH₂C₆H₄Br)·H₂O by the Rietveld method showed a lamellar arrangement similar to the methyl analogue ζ-Al(OH)(O₃PCH₃)·H₂O. Al(OH)(O₃PCH₂C₆H₄Br)·H₂O crystallises in the monoclinic system, space group P2₁/c with unit cell parameters a = 16.4972(2) Å, b = 7.0673(1) Å, c = 9.4950(2) Å and β = 113.477(1)°. Based on the powder XRD, IR and NMR data the two benzyl compounds were found to be isostructural.