3,949 research outputs found

    Crystal structures of two C,N-disubstituted acetamides: 2-(4-chlorophenyl)-N-(2-iodophenyl)acetamide and 2-(4-chlorophenyl)-N-(pyrazin-2-yl)acetamide

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    BN thanks the UGC (India) for financial assistance through a BSR one-time grant for the purchase of chemicals.In the crystal of 2-(4-chloro颅phen颅yl)-N-(2-iodo颅phen颅yl)acetamide, C14H11ClINO, molecules are linked by a combination of N鈥擧鈰疧 and C鈥擧鈰疧 hydrogen bonds to form a C(4)C(4)[R21(7)] chain of rings and chains of this type are linked by a combination of C鈥擟l鈰(arene) and C鈥擨鈰(arene) inter颅actions to form deeply puckered twofold inter颅woven sheets. In the crystal of 2-(4-chloro颅phen颅yl)-N-(pyrazin-2-yl)acetamide, C12H10ClN3O, mol颅ecules are linked into complex sheets by N鈥擧鈰疦, C鈥擧鈰疦 and C鈥擧鈰疧 hydrogen bonds, and by C鈥擧鈰(arene) inter颅actions.Publisher PDFPeer reviewe

    Reinvestigation of the crystal structure of it N-(4-chlorobenzylidene)-2-hydroxyaniline : a three-dimensional structure containing O鈥擧路路路N, O鈥擧路路路O and C鈥擧路路路蟺(arene) hydrogen bonds

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    MG thanks the UGC (India) for the award of a Rajeev Gandhi fellowship.The molecule of the title compound, C13H10ClNO, (I), which contains an intramolecular O鈥擧路路路N hydrogen bond, is almost planar: the dihedral angle between the two aryl rings is only 3.31 (9)掳. The molecules of (I) are linked into sheets by two C鈥擧路路路蟺(arene) hydrogen bonds and the sheets are linked into a three-dimensional structure by O鈥擧路路路O hydrogen bonds. Comparisons are made with the structures of a number of related compounds.Publisher PDFPeer reviewe

    A facile synthesis of Robinson鈥檚 NHC-stabilised diborane(4)

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    Reactions of bis(pinacolato)diboron (B2pin2) with [(IDip)AlH3] (IDip = (HCNDip)2C:, Dip = 2,6-iPr2C6H3) afforded both the new diborane [(IDip)BH2B(pin)] and the known compound [(IDip)BH2BH2(IDip)] in a facile one-pot procedure; the latter reaction is improved by the addition of free IDip. [(IDip)AlH3] transfers both IDip and hydride ligands to the diborane moiety in a halide-free approach. [(IDip)BH2B(pin)] was structurally and spectroscopically characterised and additional spectroscopic data for [(IDip)BH2BH2(IDip)] is reported.Publisher PDFPeer reviewe

    Construction of ground-state preserving sparse lattice models for predictive materials simulations

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    This work was supported primarily by the US Department of Energy (DOE) under Contract No. DE-FG02-96ER45571.First-principles based cluster expansion models are the dominant approach in ab initio thermodynamics of crystalline mixtures enabling the prediction of phase diagrams and novel ground states. However, despite recent advances, the construction of accurate models still requires a careful and time-consuming manual parameter tuning process for ground-state preservation, since this property is not guaranteed by default. In this paper, we present a systematic and mathematically sound method to obtain cluster expansion models that are guaranteed to preserve the ground states of their reference data. The method builds on the recently introduced compressive sensing paradigm for cluster expansion and employs quadratic programming to impose constraints on the model parameters. The robustness of our methodology is illustrated for two lithium transition metal oxides with relevance for Li-ion battery cathodes, i.e., Li2x Fe2(1-x)O2 and Li2x Ti2(1-x)O2, for which the construction of cluster expansion models with compressive sensing alone has proven to be challenging. We demonstrate that our method not only guarantees ground-state preservation on the set of reference structures used for the model construction, but also show that out-of-sample ground-state preservation up to relatively large supercell size is achievable through a rapidly converging iterative refinement. This method provides a general tool for building robust, compressed and constrained physical models with predictive power.Publisher PDFPeer reviewe

    Crystal structures of 2-amino-4,4,7,7-tetramethyl-4,5,6,7-tetrahydro-1,3-benzothiazol-3-ium benzoate and 2-amino-4,4,7,7-tetramethyl-4,5,6,7-tetrahydro-1,3-benzothiazol-3-ium picrate

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    BKS thanks the UGC (India) for the award of Rajeev Gandhi Fellowship.In both 2-amino-4,4,7,7-tetramethyl-4,5,6,7-tetrahydro-1,3- benzothiazol-3-ium benzoate, C11H19N2S+路C7H5O2-, (I), and 2-amino-4,4,7,7-tetramethyl-4,5,6,7-tetrahydro-1,3-benzothiazol-3-ium picrate (2,4,6-trinitrophenolate), C11H19N2S+路C6H2N3O7-, (II), the cations are conformationally chiral as the six-membered rings adopt half-chair conformations, which are disordered over two sets of atomic sites giving approximately enantiomeric disorder. For both cations, the bond lengths indicate delocalization of the positive charge comparable to that in an amidinium cation. The bond lengths in the picrate anion in (II) are consistent with extensive delocalization of the negative charge into the ring and onto the nitro groups, in two of which the O atoms are disordered over two sets of sites. In (I), the ionic components are linked by N鈥擧路路路O hydrogen bonds to form a chain of rings, and in (II), the N鈥擧路路路O hydrogen bonds link the components into centrosymmetric four-ion aggregates containing seven hydrogen bonded rings of four different types.Publisher PDFPeer reviewe

    Cation Binding Properties of Benzo-type Crown Ethers. 2. Effect of Large Ring Size upon Complexation Phenomena of Crown-7 and Crown-8 Derivatives

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    The cation-binding by two large ring-sized benzo-21-crown-7 and benzo-24-crown-8 has been performed by the solvent extraction of monovalent metal picrates (Na^+, K^+, Rb^+, Cs^+, Ag^+, and Tl^+) between water and dichlolomethane. The effect of ring size and benzo group upon the cation binding ability is discussed. The results are compared with benzo-18-crown-6 and simple unsubstituted crown ethers (18-crown-6, 21-crown-7 and 24-crown-8). It was found that large ring benzo-crown ethers have lower cation binding ability as the ring size increases compared with simple unsubstituted crown ethers while cation selectivity for large cations (Cs^+ and Tl^+) has been observed

    Cation Binding Properties of Benzo-type Crown Ethers. 3. Effect of Large Ring Size upon Complexation Phenomena of Crown-9 and Crowm-10 Derivatives

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    The cation-binding by two large ring-sized benzo-27-crown-9 and benzo-30-crown-10 has been evaluated by a solvent extraction of monovalent metal picrates (Na^+, K^+, Rb^+, Cs^+, Ag^+, and Tl^+) between water and dichlolomethane. The effect of ring size and benzo group upon the cation binding ability is discussed. The results are compared with benzo-type crown-6-8 (benzo-18-crown-6, benzo-21-crown-7 and benzo-24-crown-8) and simple unsubstituted crown-6-8 ethers (18-crown-6, 21-crown-7 and 24-crown-8) The cation-binding ability and complex formation are discussed in view of the size of the crown ether ring and the basicity of oxygen atoms
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