Volume 210, Issue 5

Cubosomes are lipid bilayer particles that can be formed by dispersing minimal surface-shaped infinite lipid bilayers in water. The structures of cubosomes of the D, G and P types of minimal surfaces are described by mathematical functions on the exponential scale, and the shape and internal structure of the calculated D-type cubosome is compared to electron microscopy studies, showing good correlation.

Ca(ReO 4 ) 2 C · (NH 2 ) 2 CO · H 2 O, M = 618.54, triclinic, a = 7.322(2) Å, b = 9.088(3) Å, c = 9.175(1) Å, α = 111.67(1), β = 91.26(1), γ = 104.89(2)°, V = 543.6(5) Å 3 , space group P [unk] (No. 2), Z = 2, D x = 3.778 g · cm −3 , μ (Mo K α ) = 23.05 cm −1 , R = 0.031 for 2104 reflections with I > 3 σ ( I ). The structure consists of ∞ 2 [MT 2 Urea ] layers which are composed of parallel chains of alternating double M–O–M (O = urea oxygen atom) and fourfold M–T–M (T = ReO 4 group) bridges. Within the layer the chains are interlinked by double M–T–M bridges. The layers are held together by H-bonds only. The coordination polyhedron of Ca is a bi(square capped) trigonal prism with Ca–O ave = 2.451(12) Å. The polyhedra are coupled into centrosymmetric dimers by sharing an edge of urea oxygen atoms.

AgTeI was obtained from stoichiometric amounts of silver and tellurium in hydroiodic acid (67%) under hydrothermal conditions. The compound crystallizes orthorhombic (space group Fddd , Z = 32, lattice constants: a = 4.868(1) Å, b = 25.00(1) Å, c = 25.73(1) Å); the refinement converged at R = 0.045 (for F obs ≥ 4 σ ( F )). The crystal structure of AgTeI is very closely related to that of the copper telluride halides CuTeX (X = Cl, Br, I). The crystal structure contains two characteristic building units: one-dimensional infinite screws of tellurium atoms and one-dimensional infinite chains of edge sharing silver tetrahedra centered by silver atoms.

The structural changes at the phase transition in NiTiO 3 have been followed by neutron powder diffraction up to 1650 K. At T c ≈ 1560 K it transforms from an (ordered) ilmenite structure ( R [unk]) to a disordered corundum like structure ( R [unk] c ) with a random distribution of the cations. Detailed Rietveld refinements including anharmonic and split-atom models revealed that the transition process is not a simple direct interchange of two neighboring cations. Each cation species occupies its own specific position in its actual oxygen octahedron. Some interstitial cation densities are found, but only in a limited temperature region. This is assigned to temperature dependent mobilities of the cations. Taking into account further the temperature variation of the sizes of various interfacial windows and tetrahedral and octahedral cavities an elementary exchange process is deduced. The difficulties in defining atomic occupancies and positions (the order parameters of the transition), when (anharmonic) atomic density distributions are present, are outlined.

YbFe 2 Al 10 crystallizes with a new structure type, which was determined from single-crystal X-ray data: Cmcm , a = 896.6(1)pm, b = 1015.3(2)pm, c = 900.3(1) pm, Z = 4, R = 0.024 for 795 structure factors and 41 variable parameters. The structure is closely related to the tetragonal ThMn 12 and CeMn 4 Al 8 type structures, from which it can be derived by substitution of some manganese by aluminum atoms, and in addition it has a different stacking of atomic layers. The ytterbium atoms have 20 neighbors (4 Fe + 16 Al), the iron atoms have distorted icosahedral coordination (2 Yb + 10 Al), and all of the five different aluminum sites are coordinated by ytterbium, iron, and aluminum atoms with coordination numbers 12, 13, and 14.

The X-ray crystal structures of the two black, isotypic, mixed valent solids In 4 Te 3 ( a = 15.619(1) Å, b = 12.749(1) Å, c = 4.4348(3) Å, space group Pnnm , Z = 4) and In 4 Se 3 ( a = 15.296(1) Å, b = 12.308(1) Å, c = 4.0806(5) Å), were redetermined using single crystals isolated from homogeneous, microcrystalline samples. X-ray powder investigations in the composition range In 4 Se 3− x S x (0 < x < 3) revealed heterogeneous samples for x > 1, indicating the non-existence of “In 4 S 3 ” under these conditions. High pressure X-ray experiments with In 4 Te 3 (powder and single crystals) and In 4 Se 3 (powder) showed pronounced anisotropies of the compressibilities for the normal pressure modifications, which can be correlated to the structure and bonding situations in both compounds. At 4.1 GPa In 4 Te 3 decomposes to In + 3InTe, the latter one crystallizing in a rocksalt structure and incorporating excess Indium in the sense In 1 + x Te. At 16.0 GPa the mixture In + 3InTe undergoes a second phase transition. In 4 Se 3 transforms to a new high pressure phase of unknown structure at 8.8 GPa.

The crystal structure of cis -[Pd{( c -C 6 H 11 ) 2 PC(S) = N(C 6 H 5 )} 2 ] has been determined at room temperature. The yellow crystals are monoclinic, space group C 2/ c with unit cell dimensions a = 19.601(2) Å, b = 8.2633(8) Å, c = 23.627(1) Å, β = 94.218(6)°, Z = 4, C 38 H 54 N 2 P 2 PdS 2 and D x = 1.342 Mg m −3 . The structure was solved by direct methods and refined by a full-matrix least-squares procedure to final R = 0.040 using 2331 reflections. The molecule is disposed about a crystallographic two-fold axis and the ( c -C 6 H 11 ) 2 PC(S) = N(C 6 H 5 ) ligand chelates the palladium atom via the thiolato S atom and the phosphino P atom such that the two sulphur atoms are cis to each other; important parameters: Pd–S 2.347(1) Å, Pd–P 2.279(1) Å and S–Pd–S 100.27(7)°.

Single crystals of L -(+)-histidine acetate dihydrate were obtained from an aqueous solution containing L -histidine and acetic acid. The crystals are triclinic with the cell dimensions, a = 8.519(3) Å, b = 9.056(4) Å, c = 9.026(3) Å, α = 61.72(3)°, β = 86.63(3)°, γ = 86.26(3)°, space group = P 1 and Z = 2. Intensities of 4725 reflections (MoK α were collected (at 123 K) using an automated four-circle diffractometer. The structure was solved using direct methods and refined to a final R index of 0.039 and R w index of 0.048 for 4423 reflections with intensities larger than 3 σ ( I ). Histidine acetate exists in the crystals as a salt where the proton from acetic acid is transfered to the imidazole ring whereas the carboxylic group is left unprotonized. The geometry of the two independent histidine molecules is nearly identical. There is an extensive system of hydrogen bonds stabilizing the structure.

The crystal structure of K 2 [5-CO 2 -2-TU] · 1.5 H 2 O, C 5 H 5 K 2 N 2 O 4.5 S, has been determined at room temperature. The colorless crystals are monoclinic, space group C 2/ c with unit cell dimensions a = 14.238(6) Å, b = 6.893(4) Å, c = 20.050(4) Å, β = 102.34(2)°, Z = 8 and D x = 1.903 Mg m −3 . The structure was solved by direct methods and refined by a full-matrix least-squares procedure to final R = 0.029 using 1494 reflections. The structure is comprised of K + cations, 5-carboxylate-2-thiouracilate dianions and water molecules in the ratio 4:2:3. The analysis shows that deprotonation of the thionucleobase occurs at the thioamide N(1) atom and at the carboxyl group. The two cations exist in seven coordinate NO 5 S geometries, one based on a pentagonal bipyramid and the other based on a capped octahedron.