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Since 1987, high-luminance low-voltage driven devices based on tris(8-hydroxyquinoline)aluminum(III) (Alq 3 ) opened the route to design low-cost large area displays and illuminators. Despite the large number of studies devoted to this material, very little is known about its basic structural and optical properties in the solid state. Therefore, we have investigated the structure(s) and the correlation between intermolecular interactions and optical properties in various Alq 3 systems, including solution, amorphous thin films, and different crystalline forms. Two novel unsolvated polymorphs of Alq 3 , namely, R-Alq 3 and -Alq 3 , have been synthesized and their crystalline structures determined from X-ray diffraction data on powders (R) and single crystals ( ). Crystals of R-Alq 3 are triclinic, space group P-1, a ) 6.2586 (8) Å, b ) 12.914(2) Å; c ) 14.743(2) Å, R ) 109.66(1)°; ) 89.66(1)°, and γ ) 97.68(1)°; crystals of -Alq 3 are triclinic, space group P-1, a ) 8.4433(6) Å, b ) 10.2522(8) Å; c ) 13.1711(10) Å, R ) 108.578(1)°, ) 97.064(1)°, and γ ) 89.743 (1)°. Both these crystal structures consist of a racemic mixture of the mer isomer, but are characterized by different molecular packings involving well-defined short contacts between quinoxaline ligands belonging to symmetry-related Alq 3 molecules with interligand spacings in the 3.5-3.9 Å range. A third "high-temperature" phase, γ-Alq 3 , was found to contain orientationally disordered mer-Alq 3 molecules, lying about a 32 position of the trigonal P-31c space group, with a ) 14.41(1) Å and c ) 6.22(1) Å. In addition, a hemichlorobenzene adduct of Alq 3 was also prepared and structurally characterized (monoclinic, space group P2 1 /n, a ) 10.786(1) Å, b ) 13.808(2) Å, c ) 16.928(2) Å, ) 97.90(2)°). Investigations of the different crystal phases, as well as of amorphous thin films and solutions by absorption, fluorescence excitation, fluorescence, and Raman spectroscopy, allowed the effect of the molecular packing on the emission properties to be elucidated, the nature of the photoexcitations to be clarified, and the vibrational fingerprints of the R and crystalline forms to be highlighted. The spectral position of fluorescence is found to be correlated with both the molecular density of the packing and the length of interligand contacts between neigboring Alq 3 molecules as a consequence of different dispersive and dipolar interactions as well as different π-π orbital overlaps (the shorter the contacts, i.e., the denser the crystal, the more the fluorescence is red-shifted). The low-temperature (4.2 K) vibronic structure of the fluorescence spectrum of Alq 3 is resolved for the first time. It is assigned to the FranckCondon activity of an in-plane bending mode at ca. 525 cm -1 , and it is symptomatic of the ligand-centered nature of the optical transitions. From the analysis of the vibronic progression the existence of a strong electronphonon coupling involving the 525 cm -1 mode with a Huang-Rhys factor of ca. 2.6 ( 0.4 is inferred. The origin of the amorp...

The accurate experimental electron density distribution of Co2(CO)6(AsPh3)2 has been determined through X-ray diffraction at T = 123 K. Metal−metal and metal−ligand bonds have been investigated by means of deformation densities and the quantum theory of atoms in molecules. The “expected” lack of charge accumulation in the deformation density map is “contradicted” by the presence of a bond critical point and a bond path line linking the two Cobalt atoms, in agreement with theoretical predictions on similar compounds. A careful analysis of the properties of ρ(r) at the bond critical points and of the Laplacian distribution along the bond paths has allowed the full characterization of all bonds in the title compound and, in particular, to discard the apparently straightforward classification of Co−Co as a closed-shell interaction. The radial shape of the atomic Laplacian makes (covalent or polar) shared interactions similar to donor−acceptor ones when at least one “heavy atom” is concerned. Thus, even if it is possible to recognize the shared character of Co−Co and As−C bonds by comparison with the donor−acceptor C−Co and As−Co interactions, this distinction is grounded on subtleties which could possibly not suffice without some a priori chemical insight.

in the production of polypropylene, the world's second-most widely produced synthetic plastic. The global demand for polypropylene has been rising continuously and its annual growth rate is expected to be 4-5% before 2020, resulting in increasing need for polymer-grade (>99.5%) propylene. [3] Nevertheless, the production of highly pure propylene represents a challenging and complicated process, which involves the separation of propylene from a propane/propylene mixture. Propane/ propylene mixtures are typically obtained by steam cracking of naphtha or during fluid catalytic cracking of gas oils in refineries, with a propylene purity of 50-60% for the former and 80-87% for the latter. Conventional separation of propane and propylene relies on cryogenic distillation, which is carried out at about 243 K and 0.3 MPa in a column containing over 100 trays. [4] Undoubtedly, this heat-driven process is highly energy-intensive.To lower the energy and operational cost and to suppress the carbon emissions associated with the propylene purification process through cryogenic distillation, several alternative technologies have been proposed and among them adsorptive separation, such as pressure/temperature swing adsorption, Adsorptive separation of olefin/paraffin mixtures by porous solids can greatly reduce the energy consumption associated with the currently employed cryogenic distillation technique. Here, the complete separation of propane and propylene by a designer microporous metal-organic framework material is reported. The compound, Y 6 (OH) 8 (abtc) 3 (H 2 O) 6 (DMA) 2 (Y-abtc, abtc = 3,3′,5,5′-azobenzene-tetracarboxylates; DMA = dimethylammonium), is rationally designed through topology-guided replacement of inorganic building units. Y-abtc is both thermally and hydrothermally robust, and possesses optimal pore window size for propane/propylene separation. It adsorbs propylene with fast kinetics under ambient temperature and pressure, but fully excludes propane, as a result of selective size exclusion. Multicomponent column breakthrough experiments confirm that polymer-grade propylene (99.5%) can be obtained by this process, demonstrating its true potential as an alternative sorbent for efficient separation of propane/propylene mixtures.

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