Neutron powder diffraction at 4.6 K and H-2 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 beta-polymorph of the hybrid organic/inorganic microporous solid aluminium methylphosphonate, Al-2(CD3PO3)(3), The methyl groups rotate rapidly at all temperatures studied in the NMR experiments, with a correlation time in the fast limit of similar to 2 x 10(-13) s and with an activation energy of similar to 10 kT 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. (C) 1999 Elsevier Science B.V. All rights reserved.</p
