| 1. |
- Casari, B. M., et al.
(författare)
-
New mixed-valence chromium structure type : NH4Cr(CrO4)(2)
- 2006
-
Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 179:1, s. 296-301
-
Tidskriftsartikel (refereegranskat)abstract
- Synthesis and crystal structure of a new structure type of mixed Cr(III)/Cr(VI) chromates is reported. NH4Cr(CrO4)(2) was prepared from CrO3 in the presence of (NH4)(2)Ce(NO3)(6). Since this is the first preparation of mixed valence ternary chromium oxides from aqueous solution, a reaction pathway for this synthesis is suggested. The crystal structure of NH4Cr(CrO4)2 has been determined from three-dimensional X-ray data collected at low temperature, 173 K. The structure belongs to the orthorhombic space group Pnma, with a = 14.5206(10), b = 5.4826(4), c = 8.7041(7) angstrom and Z = 4. The title compound consists of corner-sharing chromium(III) octahedra and chromium(VI) tetrahedra forming a three-dimensional network with the composition [Cr(CrO4)(2]n)(n-), containing channels in which zigzag rows of ammonium ions balance the net charge.
|
|
| 2. |
- Jansson, Jonas, 1973, et al.
(författare)
-
On the catalytic activity of Co3O4 in low-temperature CO oxidation
- 2002
-
Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 211:2, s. 387-397
-
Tidskriftsartikel (refereegranskat)abstract
- Oxidation of CO over Co3O4 at ambient temperature was studied with flow reactor experiments, and in-situ spectroscopic and structural methods. The catalyst deactivates during the reaction. The rate of deactivation increased with increasing CO or CO2 gas-phase concentration but decreased with increased 02 concentration or increased temperature. Regeneration of the catalyst in 10% O-2/Ar was more efficient than regeneration in Ar alone. The presence of carbonates and surface carbon on the deactivated catalyst was concluded from TPO experiments. None of these species could, however, be correlated with the deactivation of the catalyst. In-situ FTIR showed the presence of surface carbonates, carbonyl, and oxygen species. The change in structure and oxidation state of the catalyst was studied by in-situ XRD, in-situ XANES, XPS, and flow reactor experiments. One possible explanation for the deactivation of the catalyst is a surface reconstruction hindering the redox cycle of the reaction. (C) 2002 Elsevier Science (USA).
|
|
| 3. |
|
|
| 4. |
- Borel, Cédric, 1979, et al.
(författare)
-
Family of Isoreticular Chiral Metal-Organic Frameworks Based on Coordination and Hydrogen Bonds in [M[Co(ethylenediamine)(oxalato)2]2]
- 2010
-
Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 10:4, s. 1971-1978
-
Tidskriftsartikel (refereegranskat)abstract
- From the parent compound [Ca[Co(ethylenediamine)(oxalato)2]2]n . 4H2O, 1, a series of framework compounds was prepared via the soluble sodium salt and crystal growth with the divalent metal ions Cd2+, Mn2+, and Sr2+, (2-4). These compounds have the same general formula [M[Co(ethylenediamine)(oxalato)2]2]n . xH2O, and they all form the same four- and eight-connected 3D net having scu topology (and are thus isoreticular) with water filled channels of variable size running in one direction of the crystals. However, they crystallize in two different space groups, the chiral P21) (3, 4, and the low temperature form of 1) and the noncentrosymmetric P-4 (1 and 2). The potential voids upon water removal are 18-20% of the unit cell. Preliminary gas sorption measurements at 298 K and 8 bar show substantial CO2 and N2O uptake (12-14% and 15-16% by mass, respectively), while the H2 uptake was 0.18%, a relatively high value considering the low pressure and high temperature.
|
|
| 5. |
- Chen, HonQui, et al.
(författare)
-
Determining the crystal symmetry of epitaxial Tl-2201 thin films by X-ray diffraction
- 2002
-
Ingår i: Physica. C, Superconductivity. - 0921-4534. ; 371:2, s. 83-89
-
Tidskriftsartikel (refereegranskat)abstract
- The crystal symmetry of epitaxial Tl-2201 films on LaAlO3 and SrTiO3 substrates is investigated by X-ray diffraction. In the case of Tl1.85Ba2CuO6 film, a φ-scan of the (1 1 10) reflection showed four diffraction peaks separated by 90.00±0.02°. A 2θ-scan of the same reflection exhibited a single peak. 2Θ−ω- and φ-scans of the corresponding reflection in Tl2.04Ba2CuO6 show splitting and broadening of the diffraction peaks indicating an orthorhombic distortion. The effect of errors in film alignment on the φ-scan and 2Θ−ω-scans is discussed. A periodic function, δ=a+bsin(ω−φ), was used to correct the φ-scan measurements. The influence of lattice mismatch between film and substrate on the structural symmetry of the films is discussed.
|
|
| 6. |
- Polavarapu, Prasad, et al.
(författare)
-
Modulation and binding properties of extended glycoluril molecular clips
- 2008
-
Ingår i: New Journal of Chemistry. - : Royal Society of Chemistry (RSC). - 1369-9261 .- 1144-0546. ; 32:4, s. 643-651
-
Tidskriftsartikel (refereegranskat)abstract
- A glycoluril clip (1) provides a deep cavity for binding of guest molecules. Guest species interactpreferentially via hydrogen bonding or ion–lone pair interactions. Complexation-inducedconformational modulation of the cavity wall distance was observed. At higher guest–host ratios,inclusion compounds with organic guest molecules are obtained. The X-ray crystallographicstructure of 1.(NH4PF6).3CHCl3.2CH3OH shows formation of a network of clips connected viapolar and non-polar interactions.
|
|
| 7. |
- Erdelyi, Mate, 1975, et al.
(författare)
-
Insight into β -hairpin stability: a structural and thermodynamic study of diastereomeric β-hairpin mimetics
- 2002
-
Ingår i: New Journal of Chemistry. - 1369-9261 .- 1144-0546. ; 26, s. 834-843
-
Tidskriftsartikel (refereegranskat)abstract
- Two diastereomers of a model β-hairpin peptide mimetic were synthesized and studied with a combination of experimental (NMR, X-ray, CD, MS, IR) and computational methods (Monte Carlo/molecular mechanics calculations). The secondary structure-stabilizing effects of hydrophobic interactions and hydrogen bonding were investigated. Comparison of the extent of folded hairpin population in non-competitive, polar aprotic, and polar protic solvents illustrates the critical role of intramolecular hydrogen bonding on hairpin stability. Investigation of 1H NMR melting curves of the diastereomeric compounds in a variety of solvents allowed an evaluation of the role of hydrophobic effects on secondary structure stabilization to be made.
|
|
| 8. |
- Öhrström, Lars, 1963, et al.
(författare)
-
An interpenetrating primitive cubic net formed by hydrogen bonds and coordination bonds in catena-poly[[bis(methanol-κO)bis(thiocyanato-κN)iron(II)]-μ-1,2-bis(4-pyridylmethylene)hydrazine-κ2N:N']
- 2008
-
Ingår i: Acta Crystallographica Section C: Crystal Structure Communications. - 0108-2701 .- 1600-5759. ; C64:8, s. m277-m279
-
Tidskriftsartikel (refereegranskat)abstract
- In the title compound, [Fe(NCS)2(C12H10N4)(CH4O)2]n, at 153(2) K, the Fe atom is located on an inversion centre, as is the centre of the N-N bond in the ligand molecule. The structure contains a one-dimensional coordination polymer with an Fe...Fe distance of 15.866(7) Å and can be described as two interpenetrating six-connected primitive cubic (pcu) three-dimensional networks when additional intermolecular O-H...S hydrogen bonds are taken into account. The compound is not isostructural with the corresponding MnII compound as they differ in the rotation around the M-O bond by 90°, giving rise to completely different hydrogen-bond patterns. This study demonstrates the impact of conformational differences on the final supramolecular arrangement.
|
|
| 9. |
- Abu-Youssef, Morsy A.M., et al.
(författare)
-
1D, 2D and 3D cadmium(II) polymeric complexes with quinoline-4-carboxylato anion, quinazoline and 2,5-dimethylpyrazine
- 2006
-
Ingår i: Polyhedron. - : Elsevier BV. - 0277-5387. ; 25:5, s. 1187-1194
-
Tidskriftsartikel (refereegranskat)abstract
- Three new cadmium(II) complexes, namely [Cd(Qux)2(H2O)]n (1), [Cd(Quz)2(N3)2]n (2) and [Cd(dmpz)(N3)2]n (3) (Qux = quinoline-4-carboxylato anion, Quz = quinazoline, dmpz = 2,5-dimethylpyrazine), have been synthesized and characterized by spectroscopic and crystallographic methods. The structure of 1 contains CdO6 slightly distorted octahedral geometry around the Cd(II) atoms, axialy coordinated to two bridging water molecules forming the 1D chain and four oxygen atoms from four different μ-O,O′-bridging caboxylato groups of (Qux) in the equatorial plane. The 1D chains are further held together through hydrogen bonds between the μ-aqua molecule and the meta non-coordinated nitrogen atom of the quinoline moiety. In complex 2, two quinazoline ligands are linked to the central Cd(II) ion in a trans position through the meta hetero nitrogen atom and di(EE), (μ1,3-N3) groups and show a two dimensional (2D) topology. In complex 3 the central cadmium(II) atom is simultaneously coordinated to di(EE), (μ1,3-N3) groups (NCdN, 180.0°) forming a sheet structure in the bc plane and further bridging μ-N,N′-dimethylpyrazine ligand in the a-direction (NCdN, 180.0°) giving rise to a 3D network structure. The IR spectra of the three complexes were measured and they confirm the X-ray structural data.
|
|
| 10. |
- Abu-Youssef, Morsy A.M., et al.
(författare)
-
1D and 2D FeII Azide Coordination Polymers with Ferromagnetic Canting
- 2008
-
Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1434-1948 .- 1099-0682. ; 2008:1, s. 112-118
-
Tidskriftsartikel (refereegranskat)abstract
- The two compounds [FeII(pyridine)2(N3)2(H2O)] (1) and [FeII(4-acetylpyridine)2(N3)2] (2) were prepared. The X-ray crystal structures show end-to-end (EE) bridging azides in both cases with a 1D Fe-NNN-Fe chain for 1 and a 2D Fe-NNN-Fe net in 2. Both compounds show similar magnetic behaviour where the high-temperature data are consistent with antiferromagnetic couplings and the low-temperature data indicate ferrimagnetic ordering based on spin canting at 20 and 45 K. Compound 2 also shows a hysteresis loop. These findings are compared to the related 3D coordination polymer [Fe(N3)2(4,4'-bipyridine)]. According to network analyses the latter compound was shown to contain the new uninodal six-connected-network topology (510 · 64 · 7)-jsm.
|
|
