A high-resolution powder synchrotron X-ray diffraction pattern of the À form of d-sorbitol has been recorded at 293 K on the BM1B beamline at the ESRF (Grenoble). The starting model of the structure was found by Monte Carlo simulated annealing. The ®nal structure was obtained through Rietveld re®nements performed with soft restraints on interatomic bond lengths and angles. The symmetry is orthorhombic, space group P2 1 2 1 2, with 12 molecules within the cell [a = 24.3012 (2), b = 20.5726 (2), c = 4.8672 (1) A Ê , V = 2433.30 (3) A Ê 3 , Z H = 3, 36 non-H independent atoms]. Crystalline cohesion between neighbouring molecules is achieved by three networks of OÐHÁ Á ÁO hydrogen bonds. The width of the Bragg peaks is interpreted through a microstructural approach in terms of anisotropic strain effects.

The powder X-ray diffraction pattern of the crystalline phase of m-toluidine has been recorded with a sensitive curved detector (CPS120) at 150 K. The structure has been solved by real-space methods (simulated annealing) followed by Rietveld re®nements with phenyl rings as rigid bodies and with soft constraints on bond lengths for peripheral atoms. The cell is monoclinic with space group P2 1 /c and Z = 8. Equivalent molecules form chains along c. The crystalline cohesion is achieved by NÐHÁ Á ÁN hydrogen bonds between neighbouring chains of non-equivalent molecules and by van der Waals interactions of neighbouring chains of equivalent molecules. The hydrogen-bonding network has been con®rmed by lattice-energy minimization. Anisotropic strain effects of the cell have been calculated. The directions of the minimal strains correspond to the directions of the hydrogen bonds. An explanation of the dif®culty to crystallize the metastable phase is given. ³ Present address: Physics Department, Atomic Energy Commission, PO Box 6091, Damascus, Syrian Arab Republic.

Treatment of N,N′-methylenedipyridinium dichloride [C5H5N-CH2-NC5H5]Cl2 with MCl2 (M = Zn or Cd) in aqueous solution gives the organic-inorganic hybrid ionic compounds [C5H5N-CH2-NC5H5] · [MCl4]. Both complex salts were fully characterised by multinuclear NMR spectroscopy, elemental analysis, and their molecular structures confirmed by powder X-ray diffraction studies. The most striking feature in both solid state structures was the presence of the C…Cl-M short contacts between the organic [C5H5N-CH2-NC5H5] dication and inorganic [MCl4] anion, which led to different crystal packing. For [C5H5N-CH2-NC5H5]·[ZnCl4], the C…Cl-Zn interactions led to the alternating arrangement of [C5H5N-CH2-NC5H5]2+[ZnCl4]2− to form 1-D chains in the direction [010], and each individual chain had a two-fold rotational axis along the b axis, while for [C5H5N-CH2-NC5H5] · [CdCl4] the C…Cl-Cd associations gave 2-D network. In both solid state structures, the presence of Cl-ring centroid distances gave a strong indication of some form of Cl-π interactions.