Browsing by Author "Malaspina, LA"

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    Fast and accurate quantum crystallography: from small to large, from light to heavy
    (American Chemical Society, 2019-10-21) Malaspina, LA; Wieduwilt, EK; Bergmann, J; Kleemiss, F; Meyer, B; Ruiz-López, MF; Pal, R; Hupf, E; Beckmann, J; Piltz, RO; Edwards, AJ; Grabowsky, S; Genoni, A
    The coupling of the crystallographic refinement technique Hirshfeld atom refinement (HAR) with the recently constructed libraries of extremely localized molecular orbitals (ELMOs) gives rise to the new quantum-crystallographic method HAR-ELMO. This method is significantly faster than HAR but as accurate and precise, especially concerning the free refinement of hydrogen atoms from X-ray diffraction data, so that the first fully quantum-crystallographic refinement of a protein is presented here. However, the promise of HAR-ELMO exceeds large molecules and protein crystallography. In fact, it also renders possible electron-density investigations of heavy elements in small molecules and facilitates the detection and isolation of systematic errors from physical effects. © 2019 American Chemical Society
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    Mapping the trajectory of proton transfer via experimental electron density
    (International Union of Crystallography (IUCr), 2017-12-01) Malaspina, LA; Sugimoto, K; Edwards, AJ; Grabowsky, S
    Hydrogen maleate (HM) salts offer the unique opportunity to follow a pseudo-reaction pathway of a proton transfer not only in theoretical simulations but also experimentally because the position of the hydrogen atom inside the strong and short intramolecular O-H···O hydrogen bond (low-barrier hydrogen bond is highly flexible dependent on the cation and/or crystalline environment (Figure 1). There is a great number of crystal structures of hydrogen maleate salts in the Cambridge Structural Database (CSD) (303 entries) which show that the O···O distance varies from 2.361 Å to 2.540 Å with a large variety of intermediate distances. Neutron diffraction studies establish that the O-H distances vary from 1.079 Å up to 1.215 Å. This means that snapshots along a pseudo-reaction pathway can be measured and, with the symmetric hydrogen bonds, even a model for a possible transition state is accessible. In this study nine different hydrogen maleate salts (4-aminopyridinium HM, 8-hydroxyquinolinium HM, barium bis-HM tetrahydrate, calcium bis-HM pentahydrate, potassium HM, lithium HM dihydrate, magnesium bis-HM hexahydrate, sodium HM trihydrate and L-phenylalaninium HM that span the whole range from perfectly symmetric to highly asymmetric intramolecular hydrogen bonds are presented. The trajectory of the proton transfer is mapped through experimental electron density (ED) studies using high-resolution low-temperature synchrotron X-ray diffraction, data measured at the beamline BL02B1 of SPring-8, Japan. For this aim, it is crucial to obtain the precise and accurate position and displacement parameters of the hydrogen atom in the low-barrier hydrogen bond. Therefore the position of the proton in all compounds presented is supported by low-temperature neutron diffraction, data measured at the beamline KOALA of the Bragg Institute of ANSTO, Australia. The response of the hydrogen atom in question to various properties, such as the experimentally derived electric field imposed by the crystallographic environment, will be discussed. © 2017 International Union of Crystallography
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    Nickel and palladium complexes of a PP(O)P pincer ligand based upon a peri-substituted acenaphthyl scaffold and a secondary phosphine oxide
    (American Chemical Society, 2022-05-24) Duvinage, D; Puylaert, P; Wieduwilt, EK; Malaspina, LA; Edwards, AJ; Lork, E; Mebs, S; Hupf, E; Grabowsky, S; Beckmann, J
    A PP(O)P pincer ligand based upon a peri-substituted acenaphthyl (Ace) scaffold and a secondary phosphine oxide, (5-Ph2P-Ace-6-)2P(O)H, was prepared and fully characterized including a neutron diffraction study. The reaction with [Ni(H2O)6]Cl2and PdCl2produced ionic metal(II) complexes [κ3-P,P',P''((5-Ph2P-Ace-6-)2P(OH))MCl]Cl, which upon addition of Et3N gave rise to zwitterionic metal(II) complexes κ3-P,P',P''((5-Ph2P-Ace-6-)2P(O))MCl (M = Ni, Pd). The reaction with Ni(COD)2(COD = cyclooctadiene) provided the η3-cyclooctenyl Ni(II) complex κ3-P,P',P''((5-Ph2P-Ace-6-)2P(O))Ni(η3-C8H13). A detailed complementary bonding analysis of the P-H, P-O, and P-M interactions was carried out (M = Ni, Pd). © 2022 American Chemical Society.