Volume 211, Issue 12

The B 12 unit of zirconium dodecaboride has been reported as an icosahedron according to the Inorganic Crystal Structure Data Base, whereas the reference work actually confirmed a cubeoctahedral arrangement for B 12 . Convergent beam electron diffraction was applied to verify the latter and original assignment.

Cubic lipid bilayer structures described as vibrating standing waves centered on a nodal surface can explain various dynamic phenomena, like cubosome formation and vesicle budding-off. This description has been extended to the two-dimensional cell membrane. It is demonstrated how this standing wave conformation model of the cell membrane can provide control of membrane transport processes in space and time. The significance of lipid composition to give the appropriate elastic rigidity is discussed in relation to present knowledge of membrane lipid molecular shape.

Bøggild intergrowth of an intermediate plagioclase from Ylämma, Finland was investigated by high resolution transmission electron microscopy. A quantitative chemical analysis was carried out on the exsolution lamellae by means of an energy dispersive analyzer. The chemical compositions of the two alternating phases were determined by point analysis to Ab 38.7 An 60.1 Or 1.2 and Ab 51.0 An 46.8 Or 2.2 for the thicker and the thinner lamellae, respectively. The bulk chemical composition Ab 42.0 An 56.5 Or 1.5 calculated from the thickness of lamellae was consistent with that determined by X-ray microprobe analysis except for Or contents. Continuous resolution of lattice fringes across exsolution lamellae shows matching of lattices, which is consistent with the compositional difference in the exsolution lamellae.

The title compounds were prepared from the elements in sealed tantalum tubes at 1320 K and subsequent annealing at 970 K. EuZnIn adopts the CeCu 2 structure (space group Imma ) with a random distribution of the Zn and In atoms on the Cu position. EuPtIn and EuZnSn crystallize with the ordered CeCu 2 structure (space group Pnma ). The three structures were refined from single crystal X-ray diffractometer data: a = 482.3(1) pm, b = 780.7(2) pm, c = 827.6(2) pm, wR 2 = 0.0773, 367 F 2 values and 13 variables for EuZnIn, a = 746.94(8) pm, b = 447.27(6) pm, c = 843.46(9) pm, wR 2 = 0.0689, 381 F 2 values and 20 variables for EuPtIn, and a = 789.4(1) pm, b = 476.7(1) pm, c = 807.9(1) pm, wR 2 = 0.0955, 474 F 2 values and 20 variables for EuZnSn. The site occupancies for the transition metal and indium (tin) atoms are different in EuPtIn and EuZnSn. The more electronegative atoms, Pt and Sn, occupy the energetically favored positions with the maximum Pt – Pt and Sn – Sn separation in the rhombus of the [PtIn] and [ZnSn] polyanions. The crystal chemistry and chemical bonding of EuZnIn, EuZnSn, and EuPtIn is discussed in comparison with other intermetallic europium compounds, all of which crystallize with structures related to CeCu 2 and TiNiSi.

From neutron powder diffraction intensities it is often problematic to distinguish between centrosymmetry and non-centrosymmetry. X-ray single crystal diffraction may be more accurate. In this paper we compare refinement results of crystal structures on the basis of neutron powder data of orthorhombic NdGaO 3 (300 K) and of rhombohedral LaGaO 3 (573 K), obtained from non-centrosymmetric and centrosymmetric starting models. By using of X-ray single crystal measurements, the structures of LaGaO 3 and NdGaO 3 could be determined as being centrosymmetric corresponding to the space group R [unk] c and Pbnm , respectively.

The crystal structure of ammonium dodecaoxodiperoxotetramolybdate(VI)-water (1/2), (NH 4 ) 4 [Mo 4 O 12 · (O 2 ) 2 ] · 2H 2 O, has been determined from single-crystal X-ray diffraction data. The yellow compound crystallizes in the monoclinic space group P 2 1 / m with a = 8.401(1) Å, b = 8.819(1) Å, c = 12.802(1) Å, β = 100.01(1)°, V = 934.1 (2) Å 3 and Z = 2. Full matrix least-squares refinement of 179 structural parameters gave R = 0.031 ( R w = 0.048) for 2161 observed [ I > 3 σ ( I )], independent reflections. The anions are disordered in the crystals but the disorder could be resolved. In the [Mo 4 O 12 (O 2 ) 2 ] 4− anion the four molybdenum atoms form almost a square and are six-coordinated in a distorted octahedral manner by oxygen atoms. Each peroxo group is coordinated to all four molybdenum atoms and each molybdenum atom is coordinated to two bridging oxy oxygen atoms, two bridging peroxo oxygen atoms and two terminal oxygen atoms. The anion has approximately D 2d symmetry and has a structure unusual for peroxometallates. Selected bond distances: Mo–O peroxo 2.233(3) Å–2.247(3) Å, Mo = O terminal 1.694(4) Å–1.740(4) Å, Mo–O bridging 1.918(3) Å–1.945(2) Å and (O–O) peroxo 1.457(6) Å–1.462(5) Å. Mo…Mo is 3.2727(5) Å, 3.2850(6) Å and 3.2870(6) Å.

The title compound C 25 H 21 FSn crystallizes in the orthorhombic system, space group Pbca , with a = 20.172 (2) Å, b = 26.732 (2) Å, c = 7.766 (1) Å, Z = 8. The molecular structure shows an almost undistorted tetrahedral coordination about Sn and a propeller-like conformation of the SnPh 3 group, the conformation of the para -substituted benzyl moiety is strongly controlled by the configuration of the SnPh 3 group. Physical properties of C 25 H 21 FSn are explained in terms of structural data. The crystal structure has been refined to R = 0.024 for 2435 observed reflections.

Large single crystals of optical quality of betaine hydrogen dihydrogen iodate have been grown from aqueous solutions. An X-ray structure analysis yields space group P [unk], a 1 = 6.232(1) Å, a 2 = 9.478(1) Å, a 3 = 12.252(2) Å, α 1 = 87.94(1)°, α 2 = 84.59(1)°, α 3 = 85.88(1)°, Z = 2, Q calc = 2.982g cm −3 , Q obs = 2.977 g cm −3 . The structure consists of puckered layers which are built up from edge- and corner-sharing [IO 6 ] and [IO 7 ] polyhedra, respectively. Between adjacent layers van der Waals interactions are important. The complete elastic stiffness tensor was determined by the aid of ultrasonic methods. The tensors of thermoelastic constants and thermal expansion have been studied in the range between 290 K and 350 K. Both the elastic properties and the thermal expansion exhibit a distinct anisotropy, which is closely related to the anisotropy of the structural bonding system. No electric conductivity could be detected near room temperature.

( μ -Br)( μ -PH 2 )Mn 2 (CO 8 ) ( I ) and ( μ -PH 2 ) 2 · Mn 2 (CO 8 ) ( II ) co-crystallize in space group P2 1 / c with a = 9.467(2) Å, b = 12.181(2) Å, c = 13.086(3) Å, β = 109.98(2)°, V = 1418.2(5) Å 3 . The Mn 2 (CO) 8 part of both molecules occupies the same site, the positions of the bromo and phosphido bridges show positional disorder. Average bond lengths are Mn–Br 2.606(5) Å and Mn–P 2.321(8) Å.

At room temperature, tris(ethyldimethylphenylammonium)tri- μ -chlorohexachlorodibismuthate(3-), C 30 H 48 · Bi 2 Cl 9 N 3 , crystallizes in the monoclinic space group ( C 2 h 5 ; P 2 1 / c , (No. 14); a = 1799.7(3) pm, b = 1307.6(2) pm, c = 1781.9(4)pm, β = 92.72(2)°, Z = 4, D x = 1.883 g/cm 3 . The structure consists of ethyldimethylphenylammonium cations and binuclear chlorobismuthate(III) anions formed by two face-sharing BiCl 6 , octahedra. The compound has an irreversible phase transition at 363 K with an enthalpy of 13.35 kJ mol −1 and melts at 478 K.

Diphenyltin dichloride · diphenylcyclopropenone crystallizes in the monoclinic P 2 1 / n space group ( a = 12.322(4) Å, b = 11.370(2) Å, c = 16.676(4) Å, β = 95.54(1)°) and tri( p -chlorophenyl)tin chloride · diphenylpropenone in the orthorhombic Pbca space group ( a = 25.603(2) Å, b = 9.811(1) Å, c = 25.425(2) Å). The five-coordinate tin atom in both complexes shows trigonal bibyramidal coordination.

The structures of two [2 π + 2 π ] cycloaddition adducts, [ endo -3- exo -cyano-7-methoxytricyclo[4.2.1.0 2.5 ]-non-7-ene and dimethyl exo , endo -5-aza-tetracyclo-[7.2.1.0 2.8 .0 3.7 ]dodec-10-ene-4,6-dione-10,11-dicarboxylate, were determined and the stereo- and regiochemistry of each molecule was established. One adduct possesses an endo ring fusion while the other was found to be exo . In both structures molecules form centrosymmetric dimers as a result of weak intermolecular, non-bonded interactions of the type C=O…H–C.