Search

Alkyl chains of varied length and steric bulk are generally appended to π-conjugated chromophores to increase solubility. These alkyl chains also regulate many aspects of the solid-state packing an...

New layered structures corresponding to the general formula [PbBiO2]A(n+1)B(n)O(3n-1)Cl(2) Were prepared. Pb5BiFe3O10Cl2 (n = 3) and Pb5Bi2Fe4O13Cl2 (n = 4) are built as a stacking of truncated A(n+1)B(n)O(3n-1) perovskite blocks and alpha-PbO-type [A(2)O(2)](2+) (A = Pb, Bi) blocks combined with chlorine sheets. The alternation of these structural blocks can be represented as an intergrowth between the hematophanite and Sullen-type structural blocks. The crystal and-Magnetic structures of Pb5BiFe3O10Cl2 and Pb5Bi2Fe4O13Cl2 were investigated in the temperature range of 1.5-700 K using X-ray and neutron powder diffraction, transmission electron microscopy and Fe-57 Mossbauer spectroscopy. Both compounds crystallize in the I4/mmm space group with the unit cell parameters a approximate to a(p) approximate to 3.92 angstrom (a unit-cell parameter of the perovskite-structure), c approximate to 43.0 angstrom for the n = 3 member and c approximate to 53.5 angstrom for the n = 4 member. Despite the large separation between the slabs containing the Fe3+ ions (nearly 14 angstrom), long-range antiferromagnetic order sets in below similar to 600 K with the G-type arrangement of the Fe magnetic moments aligned along the c-axis. The possibility of mixing d(0) and d(n) cations at the B sublattice of these structures was also demonstrated by preparing the Ti-substituted n = 4 member Pb6BiFe3TiO13Cl2.

Ge5O11H[C6N2H13] has been hydrothermally synthesized. The structure of the material has been determined by single-crystal X-ray diffraction. This novel layered germanate consists of an alternation of [Ge5O11H]− inorganic sheets and monoprotonated 1,4-diazabicyclo-[2,2,2]-octane molecules. It exhibits an arrangement of 4- and 10-ring in infinite layers not observed before. The catalytic activity in Michael reactions has been tested showing that the addition occurs at the amine centers in the interlayer space. Reuse of the catalyst and the persistence of its structure after recovering has been proved.

Alternation of melting points in the series of odd- and even-numbered monoacid triacylglycerols has been known for a long time, but hitherto little experimental evidence has been available to support existing theories. In this paper the melting point alternation of β-CnCnCn-type triacylglycerols is discussed, based on the crystal structures of β-CnCnCn (n = number of C atoms per hydrocarbon chain = 10, 12, 14, 16, 18 and n = 13, described in this paper). The crystal structure of β-1,2,3-tris(tridecanoyl)glycerol (β-C13C13C13) has been determined from high-resolution synchrotron X-ray powder diffraction data and is presented here. Grid search and Rietveld refinement have been used to determine and refine the structure, respectively. Like the even-numbered monoacid triacylglycerols, β-C13C13C13 is crystallized in an asymmetric tuning-fork conformation and its acyl chains are laterally packed, resulting in a layered structure. Within a molecular layer, the odd- and even-numbered monoacid triacylglycerols are...

In search of very small band-gap polymers, we have quantum-chemically investigated the electronic structures of various polypentafulvalenes (PFVs) fused with six-membered rings. Geometrical parameters of the polymers were optimized through semiempirical Hartree−Fock band calculations at the Austin Model 1 (AM1) level. Electronic structures of the polymers were obtained through modified extended Huckel band calculations by adopting AM1-optimized geometries. It is predicted that poly(di-vinylenedioxy-pentafulvalene) and poly(di-vinylenedithia-pentafulvalene) would possess nearly zero band gaps (corresponding to λmax) despite their large bond-length alternation of ∼0.1 A. However, these polymers are expected to be very susceptible to oxidation. Poly(di-2-butenylene-pentafulvalene) and poly(dipyrazinopentafulvalene) are estimated to possess band gaps comparable with that (1.13 eV) of PFV. The calculated band gap of poly(di-ethylenedioxy-pentafulvalene) is 0.77 eV, smaller than that of PFV by 0.36 eV. We expla...

The linear (α) and nonlinear (β, γ) molecular polarizabilities of a series of donor-acceptor polyenes containing 3-8 π-bonds are studied using the semiempirical AMl parametrization and finite-field (hyper)polarizability computations as a function molecular polarization and resulting changes in bond-length alternation. Plots of α, β, and γ versus bond length alternation had similar shapes (although different magnitudes) for each chain length. The changes in α, β, and γ with molecular length were fit to exponential functions (N^m) for various bond-length alternations. These values varied over a significant range depending upon the value of bond-length alternation chosen.

The first anionic aluminophosphate molecular sieve [Al12P13O52]3-[(CH2)6N4H3]3+, denoted AlPO-CJB1, which possesses Bronsted acidity upon removing the templates, is reported. The framework is constructed from strict alternation of Al-centered polyhedra (AlO4 and AlO5) and P-centered PO4 tetrahedra by sharing oxygen atoms at vertices, which creates the anionic open-framework in contrast to previous AlPO4-n with neutral open-frameworks.