Search results for "Van der Waals"
showing 10 items of 203 documents
HP-Xe to go: Storage and Transportation of Hyperpolarized 129-Xe
2016
Abstract Recently the spin–lattice relaxation time T 1 of hyperpolarized (HP)- 129 Xe was significantly improved by using uncoated and Rb-free storage vessels of GE180 glass. For these cells, a simple procedure was established to obtain reproducible wall relaxation times of about 18 h. Then the limiting relaxation mechanism in pure Xe is due to the coupling between the nuclear spins and the angular momentum of the Xe–Xe van-der-Waals-molecules. This mechanism can be significantly reduced by using different buffer gases of which CO 2 was discovered to be the most efficient so far. From these values, it was estimated that for a 1:1 mixture of HP-Xe with CO 2 a longitudinal relaxation time of …
Metallophilic interactions in polymeric group 11 thiols
2016
Three polymeric group 11 transition metal polymers featuring metallophilic interactions were obtained directly via self-assembly of metal ions and 4-pyridinethiol ligands. In the cationic [Cu2(S-pyH)4]n2+ with [ZnCl4]n2− counterion (1) and in the neutral [Ag(S-py) (S-pyH)]n (2) 4-pyridinethiol (S-pyH) and its deprotonated form (S-py) are coordinated through the sulfur atom. Both ligands are acting as bridging ligands linking the metal centers together. In the solid state, the gold(I) polymer [Au(S-pyH)2]Cl (3) consists of the repeating cationic [Au(S-pyH)2]+ units held together by aurophilic interactions. Compound 1 is a zig-zag chain, whereas the metal chains in the structures of 2 and 3 a…
(5R)-5-[(1R)-2,2-Dichloro-1-methylcyclopropyl]-2-methylcyclohex-2-en-1-one
2011
The title compound, C(11)H(14)Cl(2)O, was synthesized by the reaction of a dichloro-methane solution of (R)-carvone and potassium tert-butano-late in the presence of a catalytic amount of benzyl-triethyl-ammonium chloride in chloro-form. The cyclo-hexene ring adopts a half-boat conformation. The cyclo-propyl ring is unsymmetrical, the shortest C-C bond being distal to the alkyl-substituted C atom. The crystal packing is stabilized only by van der Waals inter-actions.
(S)-4-(2-Chloropropan-2-yl)-1-(2,2,2-trichloroethyl)cyclohexene
2011
The title compound, C(11)H(16)Cl(4), was synthesized by the reaction of (1S)-β-pinene with triethyl-amine in the presence of ZnCl(2). The cyclo-hexene ring assumes a half-boat conformation. The crystal packing is governed only by van der Waals inter-actions. The structure, which has been refined in P2(1), presents a striking P2(1)/m pseudosymmetry.
Very close I⋯As and I⋯Sb interactions in trimethylpnictogen-pentafluoroiodobenzene cocrystals
2022
The cocrystals (CH3)3As·C6F5I (1) and (CH3)3Sb·C6F5I (2) were generated in situ from equimolar mixtures of their components. 1 and 2 show very close I⋯As and I⋯Sb directional intermolecular interactions. They are 0.5 and 0.7 Å shorter than the sums of van der Waals radii, respectively, and are the shortest C–I⋯As and C–I⋯Sb halogen bonds of this type found for experimentally characterized molecular (co)crystals. Comparisons of the packing motifs and contacts in 1 and 2 with those in (CH3)3As (3), (CH3)3Sb (4) and C6F5I (5) illustrate the occurrence and hierarchy of the specific interactions. The heteromolecular components in 1 and 2 are assembled by I⋯As, I⋯Sb and F⋯H interactions. There ar…
Crystalline gas of 1,1,1-trichloroethane
2011
Isobaric freezing of 1,1,1-trichloroethane yields crystals where all the intermolecular contacts are much longer than the sums of the van der Waals radii and only in the structure compressed to ca. 1.2 GPa do the first Cl⋯Cl contacts become commensurate with this sum. This sheds new light on the range of intermolecular interactions that are capable of controlling molecular re-orientation and arrangement.
Monolayer Formation of Molybdenum Carbonyl on Cu(111) Revealed by Scanning Tunneling Microscopy and Density Functional Theory
2012
International audience; Molybdenum carbonyl Mo(CO)(6) was adsorbed on the Cu(111) surface at 160 K in the monolayer coverage range and studied by scanning tunneling microscopy. A well-ordered monolayer of hexacarbonyl molecules was observed experimentally for the first time. The monolayer has a hexagonal structure compatible with a (root 7 x root 7)R19 superlattice on the copper (111) plane. The arrangement and orientation of the molecules on the surface were determined by density functional theory calculations, including van der Waals interactions. The comparison of adsorption and cohesive energies reveals that the molecule-substrate interaction is stronger than the intermolecular one, whi…
Cu(II) and Cu(I) complexes with 1,2-dithiosquarate as a ligand; from molecular compounds to supramolecular network structures
2008
Abstract Four new complexes of copper(II) and/or copper(I) with 1,2-dtsq as a ligand have been synthesized and characterized by single crystal X-ray diffraction methods, [CuII(terpy)(1,2-dtsq)] (1), [CuII(dmen)(1,2-dtsq)]n (2), {[CuII(dmen)2][CuI(1,2-dtsq)]2}n·2nH2O(3) and {[CuII(men)2][CuI (1,2-dtsq)]2}n·nH2O (4) (1,2-dtsq = 1,2-dithiosquarate, dianion of 3,4-dimercapto-1-cyclobutene-1,2-dione; dmen = N,N-dimethylethylenediamine; men = N-methylethylenediamine, terpy = 2,2′:6,2″-terpyridine). Compound 1 consists of neutral [CuII(terpy)(1,2-dtsq)] mononuclear units which are held together by O⋯H–C and van der Waals interactions. Compound 2 is built of neutral [CuII(dmen)(1,2-dtsq)] entities …
Synthesis and characterization of a Cu(II) complex of 2-benzylmercapto-5- methyl-1,3,4-thiadiazole (C10H10N2S 2)
2008
A Cu(II) complex of 2-benzylmercapto-5-methyl-1,3,4-thiadiazole was synthesized and characterized. The crystal structure of the copper complex and the free ligand were determined by single-crystal X-ray diffraction at room temperature: {[Cu(C10H10N2S2) 2(Cl)2], P1 triclinic, a = 8.1450(2) Å, b = 8.1690(2) Å, c = 10.8180(3) Å, α = 97.4040(12)°, β = 101.6270(11)°, γ = 116.1431(14)°; C10H10N2S2 ligand, Pbca orthorhombic, a = 8.7938(7) Å, b = 9.6491(7) Å, c = 25.3552(18) Å}. The metal complex framework consists of discrete units that provide crystalline stability through a network of van der Waals contacts. The Cu(II) is coordinated by two chloride ions and two 2-benzylmercapto-5-methyl-1,3,4- …
Synthesis, crystal structure, electrochemical and magnetic properties of (NBu4)[ReCl5(L)] with L=pyrimidine and pyridazine
2008
Abstract Two novel rhenium(IV) compounds, namely (NBu4)[ReCl5(pym)] (1) and (NBu4)[ReCl5(pyd)] (2) (pym = pyrimidine, pyd = pyridazine and NBu4 = n-tetrabutylammonium cation), have been obtained by reaction of [ReCl6]2− and the diazine in dmf, and their crystal structures determined by single-crystal X-ray diffraction. The structures of 1 and 2 consist of [ReCl5(pym)]− or [ReCl5(pyd)]− anions and NBu 4 + cations held together by electrostatic forces and van der Waals interactions. Stacking interactions are present only in 1. The coordination sphere of the ReIV ion is defined by five chloride anions and one nitrogen atom of a monodentate diazine, resulting in a distorted octahedral environme…