Karen Friese

Strategies for the structure determination of endohedral fullerenes applied to the example of Ba@C74·Co(octaethylporphyrin)·2C6H6

The structure determination of endohedral fullerenes is complicated because of the high degree of disorder which may affect the different structural components, e.g. the endohedral atom/molecule, the fullerene cage and solvent molecules. Even worse, the data-to-parameter ratio and, in particular, the scattering power is low. Different strategies are employed to deal with these problems. The observed fraction of the reciprocal lattice may be increased by means of synchrotron diffraction studies. The number of parameters may be reduced by applying rigid-body refinement strategies and by restricting the displacement parameters in the framework of the TLS approach. In the first section, we will give a short overview of the structure determinations of endohedral fullerenes from single-crystal data and discuss the severe problems one may encounter. Then we will give an example of a successful structure analysis of a metal-containing endohedral fullerene, i.e. Ba@C(74)xCo(OEP)x2C(6)H(6) (OEP = octaethylporphyrin). Several strategies of refinement, beyond the black box level, have been checked and compared, e.g. TLS, split-atom models, twin and single crystal models, anharmonic displacement parameters, and rigid-body models.

Crystal structure determination of systematically intergrown compounds: Li5(OH)2Br3 and Li2(OH)Br

Abstract We carried out a structure refinement of a crystal which was composed of two phases. Phase I was up to now unknown and corresponds to Li5(OH)2Br3 with lattice parameters a = 4.02335(1), c = 21.5638(1) Å, space group I4̅m2. Phase II is Li2(OH)Br with lattice parameters a = 4.04594(3) Å and space group Pm3̅m. The two phases have the a, b-plane in common and consequently part of the reflections overlap systematically. We performed a joint structure refinement of the two phases taking into account all reflections. The structure of Li5(OH)2Br3 is characterized by anti-perovskite like double layers of composition 2 × Li2(OH)Br, which alternate with rock-salt like layers of composition LiBr. Results for Li2(OH)Br are in good agreement with literature and confirm the correctness of the underlying model and the usefulness of the method employed in structure refinement.

[X‐(CH2)n‐]2SnBr2 (X=Cl, CN, COOCH3; n=2—4) from the Activated Element — Crystal Structure of (H3COOCC2H4)2SnBr2

Organofunctionalized alkyltin bromides have been synthesized from solvochemically activated tin metal and the corresponding alkyl bromide under mild conditions (95°C) and without the use of a catalyst. This synthetic method tolerates a variety of functional groups such as chloride, cyanide, or a carboxylic ester and can be applied to different chain lengths. Crystal structure analysis of as-prepared [(H3COOCC2H4)2SnBr2] shows a close-to-octahedral environment for the tin atom, created by intramolecular ring formation through the carbonyl groups of the two carboxylic ester functionalities. [(H3COOCC2H4)2SnBr2]: space group P21/n, Z = 4, lattice parameters at 293 K: a = 10.32501(8) A, b = 16.2350(1) A, c = 8.14838(6) A, b = 95.2319(5) °, R(F) = 0.056. The compound is isotypic to [(H3COOCC2H4)2SnCl2].

Single-crystal X-ray diffraction and electron-microscopy study of multiple-twinned Sr3(Ru0.336,Pt0.664)CuO6

Sr(3)(Ru(0.336),Pt(0.664))CuO(6) crystallizes as a monoclinic structure [space group R12/c; lattice parameters a = 9.595 (15), b = 9.595 (15), c = 11.193 (2) A and gamma = 120 degrees ]. The crystal structure is pseudotrigonal and the crystal investigated here by single-crystal X-ray diffraction was a multiple twin composed of six individuals. The twin laws are a combination of rhombohedral obverse/reverse twinning plus the threefold axis from the trigonal system. The crystal structure is related to the hexagonal perovskites. Each Pt/Ru atom is coordinated pseudo-octahedrally by O atoms, while the overall coordination polyhedra for Cu atoms can be regarded as a strongly distorted trigonal prism, where the Cu atom is clearly shifted from the center. Each [(Ru(0.336),Pt(0.664))O(6)] octahedron is connected to two Cu-O polyhedra via a common edge, and thus chains are formed parallel to the crystallographic c axis. Sr(2+) ions are incorporated between the chains and are coordinated by eight O atoms. All bond distances and angles are in good agreement with literature values. Electron-microscopy studies confirm the results from X-ray diffraction and all observed domain structures can be interpreted exactly with the established twin model. No indication of Pt/Ru ordering was found in either the X-ray or the electron-microscopy investigation.

Dilead mercury chromate(VI), Pb2HgCrO6

The structure of Pb(2)HgCrO(6) (space group P-1) can be described as consisting of isolated [CrO(4)](2-) tetrahedra and nearly linear [HgO(2)](2-) dumb-bells, which form layers of composition [HgCrO(6)](4-). These are intercalated with corrugated pseudo-hexagonal Pb(2+) layers. The Pb(2+) cation is stereochemically active and has coordination 3+5.

Twinned α-LiRb2(CF3SO3)3

The investigated crystal of alpha-LiRb(2)(CF(3)SO(3))(3) [lithium dirubidium tris(trifluoromethanesulfonate)] was a twin, with the twin matrix given by (-100/010/001). The structure consists of channel-like patterns built up of lipophilic CF(3) groups pointing towards each other. The polar interstices are occupied by cations. One Rb atom is coordinated by O atoms in the form of a distorted square antiprism, while the coordination around the second Rb atom is best described as a distorted pentagonal plane, with one O atom and one F atom situated above and an additional F atom below this plane. The O atoms around the Li atom form a strongly distorted tetrahedron.