Crystal structure

Abstract: The linear quadridentate N2S2 donor ligand 1,7-bis(N-methylbenzimidazol-2′-yl)-2,6-dithiaheptane (bmdhp) forms mono- and di-hydrate 1 : 1 copper(II) complexes which are significantly more stable toward autoreduction than those of the non-methylated analogue. The deep green monohydrate of the perchlorate salt crystallises as the mononuclear aqua-complex, [Cu(bmdhp)(OH2)][ClO4]2, in the monoclinic space group P21/n, with Z= 4, a= 18.459(3), b= 10.362(2), c= 16.365(3)A, and β= 117.14(1)°. The structure was solved and refined by standard Patterson, Fourier, and least-squares techniques to R= 0.047 and R′= 0.075 for 3 343 independent reflections with l > 2σ(l). The compound consists of [Cu(bmdhp)(OH2)]2+ ions and ClO4– counter ions. The co-ordination around copper is intermediate between trigonal bipyramidal and square pyramidal, with Cu–N distances of 1.950(4) and 1.997(4)A, Cu–O(water) 2.225(4)A, and Cu–S 2.328(1) and 2.337(1)A. In the solid state, the perchlorate dihydrate's co-ordination sphere may be a topoisomer of the monohydrate's. A new angular structural parameter, τ, is defined and proposed as an index of trigonality, as a general descriptor of five-co-ordinate centric molecules. By this criterion, the irregular co-ordination geometry of [Cu(bmdhp)(OH2)]2+ in the solid state is described as being 48% along the pathway of distortion from square pyramidal toward trigonal bipyramidal. In the electronic spectrum of the complex, assignment is made of the S(thioether)→ Cu charge-transfer bands by comparison with those of the colourless complex Zn(bmdhp)(OH)(ClO4). E.s.r. and ligand-field spectra show that the copper(II) compounds adopt a tetragonal structure in donor solvents.

Abstract: A new form of pure, solid carbon has been synthesized consisting of a somewhat disordered hexagonal close packing of soccer-ball-shaped C60 molecules. Infrared spectra and X-ray diffraction studies of the molecular packing confirm that the molecules have the anticipated 'fullerene' structure. Mass spectroscopy shows that the C70 molecule is present at levels of a few per cent. The solid-state and molecular properties of C60 and its possible role in interstellar space can now be studied in detail.

Abstract: 1. Crystal lattices. General theory 2. . Crystal lattices. Applications 3. Interaction of light with non-conducting crystals 4. Electrons in a perfect lattice 5. Cohesive forces in metals 6. Transport phenomena 7. Magnetic properties of metals 8. Ferromagnetism 9. Interaction of light with electrons in solids 10. Semi-conductors and luminescence 11. Superconductivity

Abstract: Synthese, structure et caracterisation du (1,3-bis [1-adamantyl]-2,3-dihydro)-2-carbenoimidazole prepare par deprotonation du chlorure de (1,3-bis [1-adamantyl]) imidazolium

Abstract: The crystal and molecular structure together with the hydrogen-bonding system in cellulose Iβ has been determined using synchrotron and neutron diffraction data recorded from oriented fibrous samples prepared by aligning cellulose microcrystals from tunicin. These samples diffracted both synchrotron X-rays and neutrons to better than 1 A resolution (>300 unique reflections; P21). The X-ray data were used to determine the C and O atom positions. The resulting structure consisted of two parallel chains having slightly different conformations and organized in sheets packed in a “parallel-up” fashion, with all hydroxymethyl groups adopting the tg conformation. The positions of hydrogen atoms involved in hydrogen-bonding were determined from a Fourier-difference analysis using neutron diffraction data collected from hydrogenated and deuterated samples. The hydrogen atoms involved in the intramolecular O3···O5 hydrogen bonds have well-defined positions, whereas those corresponding to O2 and O6 covered a wider v...