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Revisiting the absolute chirality and polymorphism of (–)-Istanbulin A (2020)

Arancibia, Luz ; Naspi, Mariana ; Pucci, Graciela ; [weitere]

International Union of Crystallography

In: Acta Crystallographica Section C: Structural Chemistry. 2020; 76(9): 914-920. Published 2020 Aug 28. doi: 10.1107/s2053229620011493.

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Publikationsdatum: 2020-08-28

Beschreibung: The terpenoid (−)-Istanbulin A is a natural product isolated from Senecio filaginoides DC, one of the 270 species of Senecio (Asteraceae) which occurs in Argentina. The structure and absolute configuration of this compound [9a-hydroxy-3,4a,5-trimethyl-4a,6,7,8a,9,9a-hexahydro-4H,5H-naphtho[2,3-b]-furan-2,8-dione or (4S,5R,8R,10S)-1-oxo-8β-hydroxy-10βH-eremophil-7(11)-en-12,8β-olide, C15H20O4] were determined by single-crystal X-ray diffraction studies. It proved to be a sesquiterpene lactone showing an eremophilanolide skeleton whose chirality is described as 4S,5R,8R,10S. Structural results were also in agreement with the one- and two-dimensional (1D and 2D) NMR and HR–ESI–MS data, and other complementary spectroscopic information. In addition, (−)-Istanbulin A is a polymorph of the previously reported form of (−)-Istanbulin A, form I; thus, the title compound is denoted form II or polymorph II. Structural data and a literature search allowed the chirality of Istanbulin A to be revisited. The antimicrobial and antifungal activities of (−)-Istanbulin A, form II, were evaluated in order to establish a reference for future comparisons and applications related to specific crystal forms of Istanbulins.

Digitale ISSN: 2053-2296

Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik

Publiziert von International Union of Crystallography

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Conformational polymorphism in a cobalt(II) dithiocarbamate complex (2020)

Songkerdthong, Jetnipat ; Harding, Phimphaka ; Harding, David J.

International Union of Crystallography

In: Acta Crystallographica Section C: Structural Chemistry. 2020; 76(9): 921-926. Published 2020 Aug 28. doi: 10.1107/s205322962001164x.

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Publikationsdatum: 2020-08-28

Beschreibung: Two conformational polymorphs of (N,N-dibutyldithiocarbamato-κ2 S,S′)[tris(3,5-diphenylpyrazol-1-yl-κN 2)hydroborato]cobalt(II), [Co(C45H34BN6)(C9H18NS2)] or [TpPh2Co(S2CNBu2)], 1, are accessible by recrystallization from dichloromethane–methanol to give orthorhombic polymorph 1a, while slow evaporation from acetonitrile produces triclinic polymorph 1b. The two polymorphs have been characterized by IR spectroscopy and single-crystal X-ray crystallography at 150 K. Polymorphs 1a and 1b crystallize in the orthorhombic space group Pbca and the triclinic space group P-1, respectively. The polymorphs have a trans (1a) and cis (1b) orientation of the butyl groups with respect to the S2CN plane of the dithiocarbamate ligand, which results in an intermediate five-coordinate geometry for 1a and a square-pyramidal geometry for 1b. Hirshfeld surface analysis reveals minor differences between the two polymorphs, with 1a exhibiting stronger C—H...S interactions and 1b favouring C—H...π interactions.

Digitale ISSN: 2053-2296

Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik

Publiziert von International Union of Crystallography

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C60 in a peptidic cage: a case of symmetry mismatch studied by crystallography and solid-state NMR (2020)

Gilski, Miroslaw ; Bernatowicz, Piotr ; Sakowicz, Arkadiusz ; [weitere]

International Union of Crystallography

In: Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials. 2020; 76(5): 815-824. Published 2020 Aug 29. doi: 10.1107/s2052520620009944.

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Publikationsdatum: 2020-08-29

Beschreibung: A supramolecular complex, formed by encapsulation of C60 fullerene in a molecular container built from two resorcin[4]arene rims zipped together by peptidic arms hydrogen bonded into a cylindrical β-sheet, was studied by X-ray crystallography, solid-state and solution NMR, EPR spectroscopy and differential scanning calorimetry (DSC). The crystal structure, determined at 100 K, reveals that the complex occupies 422 site symmetry, which is compatible with the molecular symmetry of the container but not of the fullerene molecule, which has only 222 symmetry. The additional crystallographic symmetry leads to a complicated but discrete disorder, which could be resolved and modelled using advanced features of the existing refinement software. Solid-state NMR measurements at 184–333 K indicate that the thermal motion of C60 in this temperature range is fast but has different activation energies at different temperatures, which was attributed to a phase transition, which was confirmed by DSC. Intriguingly, the activation energy for reorientations of C60 in the solid state is very similar for the free and encaged molecules. Also, the rotational diffusion coefficients seem to be very similar or even slightly higher for the encaged fullerene compared to the free molecule. We also found that chemical shift anisotropy (CSA) is not the main relaxation mechanism for the 13C spins of C60 in the studied complex.

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Digitale ISSN: 2052-5206

Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik

Publiziert von International Union of Crystallography

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Chemistry of transition-metal complexes containing functionalized phosphines: synthesis and structural analysis of rhodium(I) complexes containing allyl and cyanoalkylphosphines (2020)

Atencio, Reinaldo ; Chacón, Gustavo ; Mendoza, Lisbeth ; [weitere]

International Union of Crystallography

In: Acta Crystallographica Section C: Structural Chemistry. 2020; 76(9): 932-946. Published 2020 Aug 30. doi: 10.1107/s2053229620011420.

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Publikationsdatum: 2020-08-30

Beschreibung: A series of related acetylacetonate–carbonyl–rhodium compounds substituted by functionalized phosphines has been prepared in good to excellent yields by the reaction of [Rh(acac)(CO)2] (acac is acetylacetonate) with the corresponding allyl-, cyanomethyl- or cyanoethyl-substituted phosphines. All compounds were fully characterized by 31P, 1H, 13C NMR and IR spectroscopy. The X-ray structures of (acetylacetonato-κ2 O,O′)(tert-butylphosphanedicarbonitrile-κP)carbonylrhodium(I), [Rh(C5H7O2)(CO)(C8H13N2)] or [Rh(acac)(CO)(tBuP(CH2CN)2}] (2b), (acetylacetonato-κ2 O,O′)carbonyl[3-(diphenylphosphanyl)propanenitrile-κP]rhodium(I), [Rh(C5H7O2)(C15H14N)(CO)] or [Rh(acac)(CO){Ph2P(CH2CH2CN)}] (2h), and (acetylacetonato-κ2 O,O′)carbonyl[3-(di-tert-butylphosphanyl)propanenitrile-κP]rhodium(I), [Rh(C5H7O2)(C11H22N)(CO)] or [Rh(acac)(CO){tBu2P(CH2CH2CN)}] (2i), showed a square-planar geometry around the Rh atom with a significant trans influence over the acetylacetonate moiety, evidenced by long Rh—O bond lengths as expected for poor π-acceptor phosphines. The Rh—P distances displayed an inverse linear dependence with the coupling constants J P-Rh and the IR ν(C[triple-bond]O) bands, which accounts for the Rh—P electronic bonding feature (poor π-acceptors) of these complexes. A combined study from density functional theory (DFT) calculations and an evaluation of the intramolecular H...Rh contacts from X-ray diffraction data allowed a comparison of the conformational preferences of these complexes in the solid state versus the isolated compounds in the gas phase. For 2b, 2h and 2i, an energy-framework study evidenced that the crystal structures are mainly governed by dispersive energy. In fact, strong pairwise molecular dispersive interactions are responsible for the columnar arrangement observed in these complexes. A Hirshfeld surface analysis employing three-dimensional molecular surface contours and two-dimensional fingerprint plots indicated that the structures are stabilized by H...H, C...H, H...O, H...N and H...Rh intermolecular interactions.

Digitale ISSN: 2053-2296

Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik

Publiziert von International Union of Crystallography

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The X-ray constrained wavefunction of the [Mn(CO)4{(C6H5)2P-S-C(Br2)-P(C6H5)2}]Br complex: a theoretical and experimental study of dihalogen bonds and other noncovalent interactions (2020)

Van der Maelen, Juan F. ; Ceroni, Mario ; Ruiz, Javier

International Union of Crystallography

In: Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials. 2020; 76(5): 802-814. Published 2020 Aug 28. doi: 10.1107/s2052520620009889.

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Publikationsdatum: 2020-08-28

Beschreibung: The synthesis and X-ray structure determination of the [Mn(CO)4{(C6H5)2P-S-C(Br2)-P(C6H5)2}]Br complex (1) are described. The C—Br...Br dihalogen bond present in 1 has been characterized by means of topological studies of the electron density. Both the quantum theory of atoms in molecules and the electron localization function approaches have been applied to several theoretically calculated wavefunctions as well as to an X-ray constrained wavefunction. In addition, a number of theoretical techniques, such as the source function, the reduced density gradient method and the interacting quantum atoms approach, among others, have been used to analyse the dihalogen bond as well as several intramolecular interactions of the type C—H...Br—C which have also been detected in 1. The results show clearly that while bonding in the latter interactions are dominated by electrostatic components, the former has a high degree of covalency.

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Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik

Publiziert von International Union of Crystallography

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Synthesis and structures of three isoxazole-containing Schiff bases (2020)

Mason, Helen E. ; Howard, Judith A. K. ; Sparkes, Hazel A.

International Union of Crystallography

In: Acta Crystallographica Section C: Structural Chemistry. 2020; 76(9): 927-931. Published 2020 Aug 29. doi: 10.1107/s2053229620010530.

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Publikationsdatum: 2020-08-29

Beschreibung: The synthesis and structures of three isoxazole-containing Schiff bases are reported, namely, (E)-2-{[(isoxazol-3-yl)imino]methyl}phenol, C10H8N2O2, (E)-2-{[(5-methylisoxazol-3-yl)imino]methyl}phenol, C11H10N2O2, and (E)-2,4-di-tert-butyl-6-{[(isoxazol-3-yl)imino]methyl}phenol, C18H24N2O2. All three structures contain an intramolecular O—H...N hydrogen bond, alongside weaker intermolecular C—H...N and C—H...O contacts. The C—O(H) and imine C=N bond lengths were consistent with structures existing in the enol rather than the keto form. Despite having dihedral angles

Digitale ISSN: 2053-2296

Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik

Publiziert von International Union of Crystallography

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Supramolecular networks supported by the anion...π linkage of Keggin-type heteropolyoxotungstates (2020)

Panteleieva, Olha S. ; Ponomarova, Vira V. ; Shtemenko, Alexander V. ; [weitere]

International Union of Crystallography

In: Acta Crystallographica Section C: Structural Chemistry. 2020; 76(8): 753-762. Published 2020 Jul 21. doi: 10.1107/s205322962000950x.

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Publikationsdatum: 2020-07-21

Beschreibung: Anion...π interactions are newly recognized weak supramolecular forces which are relevant to many types of electron-deficient aromatic substrates. Being less competitive with respect to conventional hydrogen bonding, anion...π interactions are only rarely considered as a crystal-structure-defining factor. Their significance dramatically increases for polyoxometalate (POM) species, which offer extended oxide surfaces for maintaining dense aromatic/inorganic stacks. The structures of tetrakis(caffeinium) μ12-silicato-tetracosa-μ2-oxido-dodecaoxidododecatungsten trihydrate, (C8H11N4O2)4[SiW12O40]·3H2O, (1), and tris(theobrominium) μ12-phosphato-tetracosa-μ2-oxido-dodecaoxidododecatungsten ethanol sesquisolvate, (C7H9N4O2)3[PW12O40]·1.5C2H5OH, (2), support the utility of anion...π interactions as a special kind of supramolecular synthon controlling the structures of ionic lattices. Both caffeinium [(HCaf)+ in (1)] and theobrominium cations [(HTbr)+ in (2)] reveal double stacking patterns at both axial sides of the aromatic frameworks, leading to the generation of anion...π...anion bridges. The latter provide the rare face-to-face linkage of the anions. In (1), every square face of the metal–oxide cuboctahedra accepts the interaction and the above bridges yield flat square nets, i.e. {(HCaf+)2[SiW12O40]4−} n . Two additional cations afford single stacks only and they terminate the connectivity. Salt (2) retains a two-dimensional (2D) motif of square nets, with anion...π...anion bridges involving two of the three (HTbr)+ cations. The remaining cations complete a fivefold anion...π environment of [PW12O40]3−, acting as terminal groups. This single anion...π interaction is influenced by the specific pairing of (HTbr)+ cations by double amide-to-amide hydrogen bonding. Nevertheless, invariable 2D patterns in (1) and (2) suggest the dominant role of anion...π interactions as the structure-governing factor, which is applicable to the construction of noncovalent linkages involving Keggin-type oxometalates.

Digitale ISSN: 2053-2296

Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik

Publiziert von International Union of Crystallography

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On Cayley graphs of { b Z}^4 (2020)

Baburin, Igor A.

International Union of Crystallography

In: Acta Crystallographica Section A: Foundations and Advances. 2020; 76(5): 584-588. Published 2020 Jul 16. doi: 10.1107/s2053273320007159.

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Publikationsdatum: 2020-07-16

Beschreibung: The generating sets of { b Z}^4 have been enumerated which consist of integral four-dimensional vectors with components −1, 0, 1 and allow Cayley graphs without edge intersections in a straight-edge embedding in a four-dimensional Euclidean space. Owing to computational restrictions the valency of enumerated graphs has been fixed to 10. Up to isomorphism 58 graphs have been found and characterized by coordination sequences, shortest cycles and automorphism groups. To compute automorphism groups, a novel strategy is introduced that is based on determining vertex stabilizers from the automorphism group of a sufficiently large finite ball cut out from an infinite graph. Six exceptional, rather `dense' graphs have been identified which are locally isomorphic to a five-dimensional cubic lattice within a ball of radius 10. They could be built by either interconnecting interpenetrated three- or four-dimensional cubic lattices and therefore necessarily contain Hopf links between quadrangular cycles. As a consequence, a local combinatorial isomorphism does not extend to a local isotopy.

Digitale ISSN: 2053-2733

Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik

Publiziert von International Union of Crystallography

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Zero-obliquity twin lattice quasi-symmetry threefold twinning in 1-{(R)-1-[(3-oxo-2-isoindolinoyl)methyl]-2-propenyl}-5-methyl-2,3-indolinedione (2020)

Nespolo, Massimo ; Smaha, Rebecca W. ; Parkin, Sean

International Union of Crystallography

In: Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials. 2020; 76(4): 643-649. Published 2020 Jul 15. doi: 10.1107/s2052520620008021.

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Publikationsdatum: 2020-07-15

Beschreibung: Threefold twinning in 1-{(R)-1-[(3-oxo-2-isoindolinoyl)methyl]-2-propenyl}-5-methyl-2,3-indolinedione, C21H16N2O4, has been reported recently [Trost et al. (2020). Org. Lett. 22, 2584–2589] but the twin characterization was not published. This twinning presents several interesting features. The crystal structure is monoclinic, but its lattice is metrically strongly pseudo-orthorhombic and underpins a strongly pseudo-hexagonal sublattice. Several possible twin laws are compatible with these metric specializations, among which the one found experimentally corresponds to a trichromatic point group. Twinning is by reticular pseudo-merohedry with twin index 2 and zero obliquity but a non-zero twin misfit. The twin lattice coincides with the pseudo-hexagonal sublattice of the individual domain, which justifies the adoption of the unconventional setting B21 of the space group.

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Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik

Publiziert von International Union of Crystallography

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Low-temperature martensite relaxation in Co–Ni–Ga shape memory alloy monocrystal revealed using in situ cooling, transmission electron microscopy and low rate calorimetry (2020)

Żak, Andrzej ; Dańczak, Anna ; Dudziński, Włodzimierz

International Union of Crystallography

In: Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials. 2020; 76(4): 563-571. Published 2020 Jul 08. doi: 10.1107/s2052520620006794.

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Publikationsdatum: 2020-07-08

Beschreibung: This work presents the results of research on a Co49Ni21Ga30 magnetic shape memory single crystal. Based on a literature review, it was identified that analyses of phase transformations have been limited to specific heating and cooling rates, which could lead to an incomplete description of the resulting phenomena. Differential scanning calorimetry (DSC) performed with different heating/cooling rates enabled the precise determination of enthalpy values, which deviate from literature values. Weak and previously unnoticed thermal phenomena at temperatures below 190 K were also observed. Their presence was confirmed by low-temperature in situ transmission electron microscopy (TEM). Through DSC measurements and TEM observations, a model of the discovered phenomenon was proposed, which may have an impact on a better understanding of the physics of magnetic shape memory materials.

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Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik

Publiziert von International Union of Crystallography

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