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| 2. |
- Laniel, Dominique, et al.
(författare)
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Synthesis, crystal structure and structure-property relations of strontium orthocarbonate, Sr2CO4
- 2021
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Ingår i: Acta Crystallographica. Section B. - : International Union of Crystallography. - 2052-5192 .- 2052-5206. ; 77, s. 131-137
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Tidskriftsartikel (refereegranskat)abstract
- Carbonates containing CO4 groups as building blocks have recently been discovered. A new orthocarbonate, Sr2CO4 is synthesized at 92 GPa and at a temperature of 2500 K. Its crystal structure was determined by in situ synchrotron single-crystal X-ray diffraction, selecting a grain from a polycrystalline sample. Strontium orthocarbonate crystallizes in the orthorhombic crystal system (space group Pnma) with CO4, SrO9 and SrO11 polyhedra as the main building blocks. It is isostructural to Ca2CO4. DFT calculations reproduce the experimental findings very well and have, therefore, been used to predict the equation of state, Raman and IR spectra, and to assist in the discussion of bonding in this compound.
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| 3. |
- Makarova, Irina, et al.
(författare)
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Crystal structure, hydrogen bonds and thermal transformations of superprotonic conductor Cs6(SO4)3(H3PO4)4
- 2021
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Ingår i: Acta Crystallographica. Section B. - : International Union Of Crystallography. - 2052-5192 .- 2052-5206. ; 77:2, s. 266-274
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Tidskriftsartikel (refereegranskat)abstract
- Crystals of Cs-6(SO4)(3)(H3PO4)(4) belong to the family of alkali metal acid salts that show a high protonic conductivity at relatively low temperatures. Such properties make superprotonic crystals an excellent choice for the study of the influence of the hydrogen subsystem on the physicochemical properties and promising materials for energy-efficient technologies. Single crystals of Cs-6(SO4)(3)(H3PO4)(4) were studied by neutron diffraction methods, optical polarization microscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Neutron diffraction studies made it possible to determine the positions of all the atoms with high accuracy, including the H atom on a hydrogen bond characterized by a single-minimum potential, to confirm the chemical composition of the Cs-6(SO4)(3)(H3PO4)(4) crystals and their cubic symmetry in low- and high-temperature phases, and to draw conclusions about the three-dimensional system of hydrogen bonds, which is fundamentally different in comparison with other superprotonic compounds. Based on the experimental data obtained, crystal transformations with temperature changes are reported, and the stability of the chemical composition is shown.
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| 4. |
- Soliman, S.M., et al.
(författare)
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Towards the chemical control of molecular packing: syntheses and crystal structures of three trans-[NiL4(NCS)2] complexes
- 2014
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Ingår i: Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials. - 2052-5206 .- 2052-5192. ; 70:1, s. 115-125
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Tidskriftsartikel (refereegranskat)abstract
- Three nickel(II) isothiocyanato complexes of the formulatrans-[NiL4(NCS)2] (L = ethylisonicotinate, methylisonicotinateand 4-benzoylpyridine) have been prepared: [Ni(ethylisonicotinate)4(NCS)2] (I), [Ni(methylisonicotinate)4(NCS)2](II) and [Ni(4-benzoylpyridine)4(NCS)2] (III). All threecomplexes are monomeric and have a distorted octahedralgeometry around NiII. Despite their apparent molecularsimilarity, the crystal density of (III) (1.454 g cm 3) issignificantly higher than that of (I) and (II) (both1.408 g cm 3), suggesting that the molecular packing is mostefficient in (III). A study of the molecular Hirshfeld surfaces,together with density functional theory (DFT) calculations,provide insights into the origin of the molecular packingfeatures, and it is suggested that the greater crystal density of(III) results from smaller intermolecular electrostatic repulsions.
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| 7. |
- Ermakova, Olga, et al.
(författare)
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A combined study of the equation of state of monazite-type lanthanum orthovanadate using in situ high-pressure diffraction and ab initio calculations.
- 2014
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Ingår i: Acta Crystallographica. Section B: Structural Science, Crystal Engineering and Materials. - 2052-5206. ; 70:Pt 3, s. 533-538
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Tidskriftsartikel (refereegranskat)abstract
- Lanthanum orthovanadate (LaVO4) is the only stable monazite-type rare-earth orthovanadate. In the present paper the equation of state of LaVO4 is studied using in situ high-pressure powder diffraction at room temperature, and ab initio calculations within the framework of the density functional theory. The parameters of a second-order Birch-Murnaghan equation of state, i.e. those fitted to the experimental and theoretical data, are found to be in perfect agreement - in particular, the bulk moduli are almost identical, with values of 106 (1) and 105.8 (5) GPa, respectively. In agreement with recent reported experimental data, the compression is shown to be anisotropic. Its nature is comparable to that of some other monazite-type compounds. The softest compression direction is determined.
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| 8. |
- Hansson, Christian, et al.
(författare)
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Cis/trans isomers of PtX2L2 (X = halogen, L = neutral ligand); the crystal structure of trans-dichlorobis(dimethyl sulfide) platinum(II) and the pressure dependence of its unit-cell dimensions
- 2006
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Ingår i: Acta Crystallographica. Section B: Structural Science, Crystal Engineering and Materials. - 2052-5206. ; 62:3, s. 474-479
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Tidskriftsartikel (refereegranskat)abstract
- trans-PtCl2(dms)(2) (dms is dimethyl sulfide) crystallizes in the space group P2(1)/n and adopts the molecular point group C-i, which is the most frequently occurring point group for trans-PtX2L2 complexes (78%), as observed in the Cambridge Structural Database (CSD; 2005 release), followed by C-1 (16%). Density functional theory calculations show that the observed geometry for trans- PtCl2(dms)(2) has slightly higher energy than the most favorable geometry in the point group C-2h, but this geometry would require a space group that hampers close packing, thus showing that intermolecular forces determine the point group for the title compound. High-pressure powder diffraction studies of trans-PtCl2(dms)(2) show no phase transformation up to 8.0 GPa. The bulk modulus is 8.1 ( 6) GPa and the pressure derivative 8.1 (4). In the CSD, the number of cis- and trans-PtX2L2 compounds are almost equal, viz. 156 cis and 160 trans compounds, showing no preference for either isomer in the solid state.
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| 9. |
- Hansson, Christian, et al.
(författare)
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cis/trans isomers of PtX2L2(X=halogen, L=neutral ligand); the crystal structures of two polymorphs of cis-dichlorobis(dibenzyl sulphidokS)platinum(II) in the temperature range 100-295 K.
- 2008
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Ingår i: Acta Crystallographica. Section B: Structural Science, Crystal Engineering and Materials. - 2052-5206. ; 64:2, s. 187-195
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Tidskriftsartikel (refereegranskat)abstract
- The structures of two polymorphs, one triclinic and one monoclinic, of cis-dichlorobis(dibenzyl sulfido-kS)platinum(II), cis-PtCl2(Bz2S)2 have been determined at 295, 250, 200, 150 and 100 K. In both polymorphs the complex has a structure where platinum(II) coordinates two dibenzyl sulfide molecules and two chloro ligands, forming a complex with pseudo-sqare-planar coordination geometry. The triclinic polymorph shows disorder at all temperatures. Both polymorphs have a packing arrangement involving centrosymmetric structural dimers. cis-PtCl2(Bz2S)2 belongs to a group of complexes with the general formula PtX2L2, where X is a halogen and L is a ligand with a donor atom from groups 14, 15 or 16. The distribution of structural classes among 173 cis-PtX2L2 compounds found in the Cambridge Structural Database (CSD, Version 5.28, November 2006) has been investigated. The predominant structural class [notation according to Belsky & Zorkii (1977). Acta Cryst. A33, 1004-1006] among cis compounds is P21/c, Z=4(1) (73 structures, 42 %), followed by P-1, Z= 2(1) (33 structures, 19 %). Inversion centres combined with the screw-axis/glide plane are the dominationg packing operators (56 %) followed by the inversion centre (21 %). The cis and trans influence in cis/trans-PtCl2L2 compounds has been investigated using data from CSD. The cis.influence is small for donor atoms in groups 15 and 16. The trans influence is small for group 16 donor atoms and for nitrogen, but for phosphorus it is significantly greater than the other donor atoms studied.
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| 10. |
- Jahangiri, Amita, et al.
(författare)
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Allotwinning in a molecular crystal: (1R,3S)-dimethyl 2-oxocyclohexane-1,3-dicarboxylate.
- 2013
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Ingår i: Acta Crystallographica. Section B: Structural Science, Crystal Engineering and Materials. - 2052-5206. ; 69:Pt 5, s. 509-513
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Tidskriftsartikel (refereegranskat)abstract
- Two polytypic modifications of (1R,3S)-dimethyl 2-oxocyclohexane-1,3-dicarboxylate intergrow to form allotwins. One phase shows monoclinic symmetry, Cc, while the other is orthorhombic Pmc21. The structures may be considered as two different modes of superstructure ordering of an underlying, disordered structure. Considered in the same metrically orthorhombic unit cell a = 37.8883, b = 4.7233, c = 11.6835 Å, the two can be conveniently distinguished by their non-standard centering, Cc being represented as Xc with the centering vectors (0 0 0); (½ 0 ½); (¼ ½ ¾); (¾ ½ ¼); and Pmc21 as Xmc21 with the centering vectors (0 0 0); (½ 0 0). The difference between the allotwin domains lies only in the relationship between next-nearest neighbors along the stacking direction 100 and hence the conformations and packing efficiencies are identical for both phases and all three domains. The stacking sequences for the two phases correspond to ABAB for the orthorhombic stacking and ABA'B'/AB'A'B for the two (equivalent) monoclinic stackings. The monoclinic phase dominates comprising ca 80% of the total volume. Within the monoclinic phase, the ratio between the two possible orientations is highly unbalanced (6:1) indicating relatively large domains. The allotwinning detected in this sample may appear exotic in molecular compounds, but we suggest that the rarity of such examples in the literature is a reflection of the paucity of software that can identify and handle such cases. It is easy to overlook the possibility that a complex diffraction pattern originates from allotwinning and assume that normal mono-component twinning is the cause. The underlying mechanism in this case is the formation of two-dimensional layers of molecules that allow for two equivalent, but in terms of absolute geometry, different, ways of stacking.
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