1,721,123 research outputs found
The halogen-bonded adduct 1,4-bis(pyridin-4-yl)buta-1,3-diyne–1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8-hexadecafluoro-1,8-diiodooctane (1/1)
No full textIn the crystal structure of the title compound, C8F16I2·C14H8N2, the molecules form infinite chains parallel to [2-11] through two symmetry-independent C—I...N halogen bonds (XBs). As commonly found, the perfluoroalkyl molecules segregate from the hydrocarbon ones, forming a layered structure. Apart from the XBs, the only contact below the sum of van der Waals radii is a weak H...F contact. The topology of the network is a nice example of the paradigm of the expansion of ditopic starting modules; the XB leads to the construction of infinite supramolecular chains along [2-11] formed by alternating XB donors and acceptors
ORGANOMETALLIC FRAMEWORKS IN SUPRAMOLECULAR POLYMERS
No full textOrganometallic frameworks are useful modules in supramolecular systems creation [1]. In this respect, they can impart particular structural and electronic properties, simply by varying the ligands on the metal centre. In particular, using bifunctional ligands, it is possible to achieve infinite chains or designed supramolecular systems through the occurrence of non-covalent interactions such as hydrogen bond, halogen bond, electrostatic interaction, π-π interaction, etc. Here we report the preparation of some adducts we recently obtained on co-crystallization of trans-[PtL2(C≡C-4-py)2] (L = PCy3, PEt3) with 1,2-diiodoperfluoroethane, 1,4-diiodoperfluorobenzene and 4,4’-diiodo-2,2’,3,3’-octafluoro-trans-stilbene [2]. The halogen bond between the modules is confirmed by the X-ray structures, showing that both the organoplatinum derivative and the diiodofluorocarbons behave as bidentate and telechelic modules
[5,11,17,23-Tetra-tert-butyl-25,27-(3,6-dioxaoctan-1,8-dioxy)-26,28-bis(pyridin-2-ylmethoxy)calix[4]arene]sodium iodide–1,2,4,5-tetrafluoro-3,6-diiodobenzene–methanol (2/3/4)
No full textThe title compound, [Na(C62H76N2O 6)]I·1.5C6F4I2· 2CH3OH, is composed of five components: a calix[4]arene derivative (hereinafter C4), a sodium cation, an iodide anion, a 1,2,4,5-tetrafluoro-3,6- diiodobenzene (tFdIB) molecule and a methanol molecule in a 1:1:1:1.5:2 ratio. The complex shows several interesting features: (i) the polyoxygenated loop of C4 effectively chelates a sodium cation in the form of a distorted octahedron and separates it from the iodide counter-ion, the shortest Na +⋯I- distance being greater than 6.5 Å; (ii) the cavity of C4 is filled by a methanol molecule; (iii) a second methanol molecule is hydrogen-bonded to the N atom of a pyridinyl substituent pendant of C4 and halogen-bonded to the I atom of a tFdIB molecule; (iv) the two I atoms of another tFdIB molecule are halogen-bonded to two iodide anions, which act as monodentate halogen-bond acceptorss; (v) one of the two tFdIB molecules is located about a centre of inversion
(Tris{2-[2-(2,3,5,6-tetrafluoro-4-iodophenoxy)ethoxy]ethyl}amine)potassium iodide
No full textThe title adduct, [K(C30H24F12I 3NO6)]I, gives an extended tape of cations linked through I⋯I- halogen bonds (XBs), two of them being quite short and one quite long. In the structure, the cation is hosted in a cavity formed by the arms of the podand which presents a closed conformation wherein two tetrafluoroiodobenzene rings are near parallel [dihedral angle = 15.8 (4)°; centroid-centroid distance = 3.908 (5) Å] and the third ring is closer to orthogonal [dihedral angles = 66.28 (14) and 75.20 (19)°] to the other two rings. The coordination sphere of the K+ cation is composed of the six O atoms, the N atom and an F atom in the ortho position of one of the rings
Tetraphenylphosphonium iodide–1,3,5-trifluoro-2,4,6-triiodobenzene–methanol (3/4/1)
No full textThe crystallization of a 1:1 molar solution of 1,3,5-trifluoro-2,4,6-diiodobenzene (TFTIB) and tetraphenylphosponium iodide (TPPI) from methanol produced tetragonal needles of pure TPPI and tabular pseudo-hexagonal truncated bipyramids of the title compound, 3C24H20P+·3I−·4C6F3I3·CH4O or (TPPI)3(TFTIB)4·MeOH. The asymmetric unit is composed of six TPPI molecules, eight TFTIB molecules and two methanol molecules, overall 16 constituents. The formation of the architecture is essentially guided by a number of C—I...I− halogen bonds (XB), whose lengths are in the range 3.276 (1)–3.625 (1) Å. Layers of supramolecular polyanions are formed parallel to (10-1) wherein iodide anions function as penta-, tetra- or bidentate XB acceptors. The structure is not far from being P21/n, but the centrosymmetry is lost due to a different conformation of a single couple of cations and the small asymmetry in the formed supramolecular anion. One methanol molecule is hydrogen bonded to an iodide anion, while the second is linked to the first one via an O—H...O contact. This second methanol molecule is more loosely pinned in its position than the first and presents very high anisotropic displacement parameters and a seeming shortening of the C—O bond length. The crystal studied was refined as a perfect inversion twin
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Multinuclear Solid-State Magnetic Resonance as a Sensitive Probe of Structural Changes upon the Occurrence of Halogen Bonding in Co-crystals
Full text linkAlthough the understanding of intermolecular interactions, such as hydrogen bonding, is relatively well-developed, many additional weak interactions work both in tandem and competitively to stabilize a given crystal structure. Due to a wide array of potential applications, a substantial effort has been invested in understanding the halogen bond. Here, we explore the utility of multinuclear (13C, 14/15N, 19F, and 127I) solid-state magnetic resonance experiments in characterizing the electronic and structural changes which take place upon the formation of five halogen-bonded co-crystalline product materials. Single-crystal X-ray diffraction (XRD) structures of three novel co-crystals which exhibit a 1:1 stoichiometry between decamethonium diiodide (i.e., [(CH3)3N+(CH 2)10N+(CH3)3][2 I -]) and different para-dihalogen-substituted benzene moieties (i.e., p-C6X2Y4, X=Br, I; Y=H, F) are presented. 13C and 15N NMR experiments carried out on these and related systems validate sample purity, but also serve as indirect probes of the formation of a halogen bond in the co-crystal complexes in the solid state. Long-range changes in the electronic environment, which manifest through changes in the electric field gradient (EFG) tensor, are quantitatively measured using 14N NMR spectroscopy, with a systematic decrease in the 14N quadrupolar coupling constant (CQ) observed upon halogen bond formation. Attempts at 127I solid-state NMR spectroscopy experiments are presented and variable-temperature 19F NMR experiments are used to distinguish between dynamic and static disorder in selected product materials, which could not be conclusively established using solely XRD. Quantum chemical calculations using the gauge-including projector augmented-wave (GIPAW) or relativistic zeroth-order regular approximation (ZORA) density functional theory (DFT) approaches complement the experimental NMR measurements and provide theoretical corroboration for the changes in NMR parameters observed upon the formation of a halogen bond
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