Probing the interaction between di- and tri-functionalized carboxy-phosphonic acid and LDH layer structure

A series of carboxyphosphonate-derivatives of (Zn, Al) layered double hydroxide (LDH) was prepared and characterized by a combination of techniques including powder X-ray diffraction, FTIR spectroscopy and solid-state ¹³C CP-MAS and ³¹P MAS NMR spectroscopies. The number of carbon atoms, n=1 or 2 in HO₂C(CH₂)_nPO₃H₂, was found to have an influence on the accommodation of the interleaved molecule, the carboxylate function lying perpendicular or parallel to the inorganic sheets of the LDH host material. These observations are in agreement with NMR results which evidence an interaction of the interlayered molecules through either the carbonyl or the phosphonate group or both in the case of the larger molecule, N-(phosphonomethyl)iminodiacetic acid. The variation of the basal spacing of the hybrid materials as a function of the temperature indicates a rearrangement of the molecule within the host material gap.