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.

In order to explore the chemistry of the bidentate ligand 2,2-dimethylpropane-1,3-diyl diisocyanide and to investigate the effect of counter-ions on the polymeric structure of (2,2-dimethylpropane-1,3-diyl diisocyanide)silver(I) complexes, the title polymeric compound, [AgI(C(7)H(10)N(2))](n), was synthesized by treatment of 2,2-dimethylpropane-1,3-diyl diisocyanide with AgI. X-ray powder diffraction studies show, as expected, a polymeric structure, similar to the very recently reported Cl(-) and NO(3)(-) analogues [AgX(C(7)H(10)N(2))](n) (X = Cl(-) or NO(3)(-)). In the title structure, the Ag(I) centre is bridged to two adjacent Ag(I) neighbours by bidentate 2,2-dimethylpropane-1,3-diyl diisocyanide ligands via the NC groups to form [Ag{CNCH(2)C(CH(3))(2)CH(2)NC}](n) chains. The iodide counter-ions crosslink the Ag(I) centres of the chains to form a two-dimensional polymeric {[Ag{CNCH(2)C(CH(3))(2)CH(2)NC}]I}(n) network. This study also shows that this bidentate ligand forms similar polymeric structures on treatment with AgX, regardless of the nature of the counter-ion X(-), and also has a strong tendency to form polymeric complexes rather than dimeric or trimeric ones.

In order to explore the potential propensity of the 1,1'-methylenedipyridinium dication to form organic-inorganic hybrid ionic compounds by reaction with the appropriate halide metal salt, the organic-inorganic hybrid salts 1,1'-methylenedipyridinium tetrachloridocuprate(II), (C(11)H(12)N(2))[CuCl(4)], (I), and 1,1'-methylenedipyridinium bis[tetrachloridoaurate(III)], (C(11)H(12)N(2))[AuCl(4)](2), (II), were obtained by treatment of 1,1'-methylenedipyridinium dichloride with CuCl(2) and Na[AuCl(4)], respectively. Both hybrid salts were isolated as pure compounds, fully characterized by multinuclear NMR spectroscopy and their molecular structures confirmed by powder X-ray diffraction studies. The crystal structures consist of discrete 1,1'-methylenedipyridinium dications and [CuCl(4)](2-) and [AuCl(4)](-) anions for (I) and (II), respectively. As expected, the dications form a butterfly shape; the Cu(II) centre of [CuCl(4)](2-) has a distorted tetrahedral configuration and the Au(III) centre of [AuCl(4)](-) shows a square-planar coordination. The ionic species of (I) and the dication of (II) each have twofold axial symmetry, while the two [AuCl(4)](-) anions are located on a mirror-plane site. Both crystal structures are stabilized by intermolecular C-H···Cl hydrogen bonds and also by Cl···π interactions. It is noteworthy that, while the average intermolecular centroid-centroid pyridinium ring distance in (I) is 3.643 (8) Å, giving strong evidence for noncovalent π-π ring interactions, for (II), the shortest centroid-centroid distance between pyridinium rings of 5.502 (9) Å is too long for any significant π-π ring interactions, which might be due to the bulk of the two [AuCl(4)](-) anions.

Crotonaldehyde semicarbazone and crotonaldehyde thio­semicarbazone show the same E conformation around the imine C=N bond. Each mol­ecule has an intra­molecular N—H⋯N hydrogen bond, which generates an S(5) ring. Inter­molecular N—H⋯O hydrogen bonds in the semicarbazone link the mol­ecules into layers parallel to the bc plane, while weak inter­molecular N—H⋯S hydrogen bonds in the thio­semicarbazone link the mol­ecules into chains propagating in [110].

In the title compound, [AgBr(C7H10N2)]n, adjacent Ag(I) atoms are bridged by bidentate CNCH2C(CH3)2CH2NC ligands via the NC groups, forming [Ag{CNCH2C(CH3)2CH2NC}]n chains with the metal atom in a distorted tetrahedral coordination. The bromide counter-anions cross-link the Ag(I) atoms of the chains, forming a two-dimensional polymeric network {[AgI(CNCH2C(CH3)2CH2NC)]Br}n extend­ing parallel to (010). The polymeric structure is similar to that of the very recently reported Cl−, I− and NO3 − analogues. This gives a strong indication that 2,2-dimethyl­propane-1,3-diyl diisocyanide is a potential ligand for giving polymeric structures on treatment with AgX (X = Cl−, Br−, I− or NO3 −) regardless of the counter-anion used.

The title compound, C(12)H(10)F(3)NO(2), an important precursor in the preparation of benzovesamicol analogues for the diagnosis of Alzheimer's disease, was prepared by the epoxidation of 5,8-dihydronaphthalen-1-amine using 3-chloroperoxybenzoic acid. The structure was determined by X-ray powder diffraction, multinuclear NMR spectroscopy and FT-IR spectroscopy. A pair of molecules form intermolecular N-H...O hydrogen bonds, involving the amino and oxirene groups, to produce a dimer.