Structure and dynamics of methyl groups in the deuterated microporous organic–inorganic hybrid, aluminium methylphosphonate-β

Neutron powder diffraction at 4.6 K and 2H NMR spectroscopy over the range 100–400 K have been used to examine the structure and rotational dynamics of CD3 groups pointing into the unidimensional channels of the β-polymorph of the hybrid organic/inorganic microporous solid aluminium methylphosphonate, Al2(CD3PO3)3. The methyl groups rotate rapidly at all temperatures studied in the NMR experiments, with a correlation time in the fast limit of ∼2×10−13 s and with an activation energy of ∼10 kJ mol−1. Extrapolation to 4.6 K indicates that the groups will be stationary and this is confirmed by the neutron diffraction experiment, where the lowest-energy configurations of the methylphosphonate groups are all found to have the methyl deuterons staggered with respect to the phosphonate oxygens.