| 1. |
- Fahlquist, Henrik, 1983-, et al.
(författare)
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Cs10H[Ga3H8]3 : A Hydrogenous Zintl Phase Containing Propane-Like Polyanions [Ga3H8]3- and Interstitial Hydrogen
- 2013
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 52:12, s. 7125-7129
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Tidskriftsartikel (refereegranskat)abstract
- The hydrogenous Zintl-phase Cs10H[Ga3H8](3) containing propane-like polyanions [Ga3H(D)(8)](3-) was successfully synthesized by direct hydrogenation of a 1:1 Cs/Ga metal mixture and characterized by powder X-ray and neutron diffraction. The charge of the polyanions is balanced by two different species of cations, hydrogen-centered octahedra [H(D)Cs-6](5+) and isolated Cs+. The structure crystallizes in the hexagonal space group P6(3)/mcm (193) with the cell parameters a = 11.1108(3) angstrom, c = 18.2149(5) angstrom, Z = 2.
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| 2. |
- Fahlquist, Henrik, 1983-, et al.
(författare)
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SrH2Mg2[Co(I)H5], BaH2Mg5[Co(-I)H4]2 and RbH2Mg5[Co(-I)H4 Ni(0)H4] illustrate how small variations in counter ions are important for the solid state stabilization of 3d-transition metal hydrido complexes as well as influencing electrical and magnetic properties
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Variations in the counter ion support to low valent 3d transition metal hydrido complexes in solids state hydrides influence formal oxidation states as well as their electrical properties. In a combined study using neutron scattering and first principle calculations a very low formal oxidation state of (-I) can be described for cobalt in a slightly distorted tetrahedral Co(-I)H4-complex in BaH2Mg5[Co(-I)H4]2 and in the structurally closely related RbH2Mg5[Co(-I)H4 Ni(0)H4]. This indicates that the electron “back donating” effect via the polarisable hydride ions to the counter ions in the solid state hydrides, can be compared to more conventional “back bonding” and reduce the oxidation state down to -I. The hydrides were synthesised by hot sintering of transition metal powders with the corresponding binary alkali- and alkaline earth hydrides. In the similarly synthesized SrH2Mg2[Co(I)H5] cobalt is formally +I-valent, showing a high sensitivity to subtle differences in the counter ion framework.
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| 3. |
- Fahlquist, Henrik, et al.
(författare)
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Stabilization of 3d Transition Metal Hydrido Complexes in SrH2Mg2[Co(I)H-5], BaH2Mg5[Co(-I)H-4](2), and RbH2Mg5[Co(-I)H4Ni(0)H-4] via Easily Polarizable Hydride Ligands
- 2016
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 55:7, s. 3576-3582
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Tidskriftsartikel (refereegranskat)abstract
- A combined study using neutron diffraction, inelastic neutron scattering, and first-principles calculations describe cobalt with a very low formal oxidation state of (-I) in a slightly distorted tetrahedral Co(-I)H-4-complex in BaH2Mg5[Co(-I)H-4](2) and in the structurally related RbH2Mg5[Co(-I)H4Ni(0)H-4]. This indicates that the electron back donating effect via the polarizable hydride ions to the counterions in the solid state hydrides, can be compared to more conventional back bonding able to reduce the oxidation state down to -I. The hydrides were synthesized by hot sintering of transition metal powders with corresponding binary alkali- and alkaline earth hydrides. In the similarly synthesized SrH2Mg2[Co(I)H-5], cobalt is formally + I-valent, showing a high sensitivity to differences in the counterion framework, which can also influence electrical properties.
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| 4. |
- Fahlquist, Henrik, et al.
(författare)
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Structural characterization of Sr4Mg4H4[CoH5](3) shows the importance of support from polarizing counter ions to 3d transition metal hydrido complexes
- 2013
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 579, s. 31-33
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Tidskriftsartikel (refereegranskat)abstract
- The structure of the title compound was refined from neutron powder diffraction data in the cubic space group P-43m (215). The unit cell contains one formula unit with 3 structurally equivalent [Co(I)H-5](4)-complexes as well as 4 interstitial hydride (H-) ions. The presence of the larger and less polarizing Sr2+ ions weakens the bond in the complexes and probably also the stability of the structure. Attempts to synthesize the corresponding Ba analogue failed in contrast to using smaller and more polarizing Ca2+ and Yb2+ counterions.
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| 5. |
- Fahlquist, Henrik, 1983-
(författare)
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Transition Metal Hydride Complexes and Hydrogenated Gallium Clusters : Synthesis and Structural Properties
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Synthesis and structural characterisation of metal hydrides in two important systems are presented. The first system presented is low valent cobalt and nickel complex hydrides with the compositions BaMg5Co2H10, RbMg5CoNiH10, SrMg2CoH7and Sr4Mg4Co3H19 featuring nickel with oxidation state of 0 and cobalt with oxidation state +I and -I. The second system presented is polyanionic gallium complex hydrides with the compositions RbGaH2, RbxK(1−x)GaH2 (0.5≤x≤1), CsxRb(8−x)Ga5H15 (0≤x≤8) and Cs10Ga9H25 featuring novel hydrogenous polyanionic gallium hydride clusters mimicking common hydrocarbons. The syntheses of the compounds were performed at elevated temperatures and at moderate hydrogen pressures (50-100 bar). The structural investigations were mainly done by X-ray powder diffraction (XRPD) and neutron powder diffraction (NPD). The metal-hydrogen bond was investigated by vibrational spectroscopy using Fourier Transform IR-spectroscopy (FTIR) and Inelastic Neutron Scattering (INS).By subtle changes in the compositions of the hydrides it was possible to induce major changes in band gaps, oxidation states and structures.
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| 6. |
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| 7. |
- Fahlquist, Henrik, et al.
(författare)
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Varying the Alkali-Metal Radii in (KxRb1−x)n[GaH2]n (0 ≤ x ≤ 1)Reorients a Stable Polyethylene-Structured [GaH2]nn− Anionic Chain
- 2013
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 52:9, s. 4771-4773
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Tidskriftsartikel (refereegranskat)abstract
- The stability of a negatively chargedpolyethylene-structured [GaH2]nn−cluster ion was inves-tigated by varying the K+/Rb+ratio in (KxRb1−x)n[GaH2]n(0≤x≤1). Neutron, X-ray, and IR spectroscopies wereused to characterize the new phases. Between the limitingcompositions Kn[GaH2]nand Rbn[GaH2]n, the [GaH2]nn−chains remained almost identical, indicating a stable specie.For rubidium-rich samples up to a potassium contentcorresponding to (K0.5Rb0.5)n[GaH2]n, two phases coexistin the samples, RbGaH2and (K0.5Rb0.5)n[GaH2]n, with aratio mirroring the relative alkali-ion content. The twophases have a different alignment of the [GaH2]nn−chains.For potassium-rich samples beyond (K0.5Rb0.5)n[GaH2]n,the samples were single-phased. The unit cell volume ofthe new (K0.5Rb0.5)n[GaH2]nstructure type shrinksaccording to Vegard’s law as smaller K+ions substitutefor larger Rb+ions. The [GaH2]nn−chains remained,however, almost identical. IR spectra from the differentphases were very similar, exhibited stretching, scissoring,and rocking modes similar to those in ordinary poly-ethylene, but shifted to lower frequencies, reflectingweaker Ga−H bonds. The existence of stable Kn[GaH2]nand Rbn[GaH2]n, would help to dehydrogenate KGaH4and RbGaH4upon heating. If this could be transferred tolighter alanates and borohydrides, it could be possible todevelop more functional hydrogen-storage systems.
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| 8. |
- Inge, A. Ken, et al.
(författare)
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Solving complex open-framework structures from X-ray powder diffraction by direct-space methods using composite building units
- 2013
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Ingår i: Journal of applied crystallography. - 0021-8898 .- 1600-5767. ; 46, s. 1094-1104
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Tidskriftsartikel (refereegranskat)abstract
- The crystal structure of a novel open-framework gallogermanate, SU-66 {|(C6H18N2)(18)(H2O)(32)|[Ga4.8Ge87.2O208]}, has been solved from laboratory X-ray powder diffraction (XPD) data by using a direct-space structure solution algorithm and local structural information obtained from infrared (IR) spectroscopy. IR studies on 18 known germanates revealed that the bands in their IR spectra were characteristic of the different composite building units (CBUs) present in the structures. By comparing the bands corresponding to Ge-O vibrations in the IR spectra of SU-66 with those of the 18 known structures with different CBUs, the CBU of SU-66 could be identified empirically as the Ge-10(O,OH)(27) cluster (Ge-10). The unit cell and space group (extinction symbol P--a; a = 14.963, b = 31.593, c = 18.759 angstrom) were determined initially from the XPD pattern and then confirmed by selected-area electron diffraction. The structure of SU-66 was solved from the XPD data using parallel tempering as implemented in FOX [Favre-Nicolin & Cerny (2002). J. Appl. Cryst. 35, 734-743] by assuming P2(1)ma symmetry and two Ge-10 clusters in the asymmetric unit. Rietveld refinement of the resulting structure using synchrotron XPD data showed the framework structure to be correct and the space group to be Pmma. The framework has extra-large (26-ring) onedimensional channels and a very low framework density of 10.1 Ge/Ga atoms per 1000 angstrom(3). SU-66, with 55 framework atoms in the asymmetric unit, is one of the more complicated framework structures solved from XPD data. Indeed, 98% of the reflections were overlapping in the XPD pattern used for structure solution. Tests on other open-framework germanates (SU-62, SU-65, SU-74, PKU-12 and ITQ-37) for which the XPD data, unit cell, space group and IR spectra were available proved to be equally successful. In a more complex case (SU-72) the combination of FOX and powder charge flipping was required for structure solution.
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| 9. |
- Mink, Janos, et al.
(författare)
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Vibrational properties of -KSiH3 and -RbSiH3 : a combined Raman and inelastic neutron scattering study
- 2017
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Ingår i: Journal of Raman Spectroscopy. - : Wiley. - 0377-0486 .- 1097-4555. ; 48:2, s. 284-291
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Tidskriftsartikel (refereegranskat)abstract
- The hydrogen storage materials ASiH(3) (A=K and Rb) represent complex metal hydrides built from metal cations and pyramidal SiH3- ions. At room temperature, SiH3- moieties are randomly oriented because of dynamical disorder (-modifications). At temperatures below 200K, ASiH(3) exist as ordered low-temperature () modifications. The vibrational properties of -ASiH(3) were characterized by a combination of Raman spectroscopy and inelastic neutron scattering. Internal modes of SiH3- are observed in the spectral range 1800-1900cm(-1) (stretching modes) and 890-1000cm(-1) (bending modes). External modes are observed below 500cm(-1). Specifically, SiH3- librations are between 300-450cm(-1) and 270-400cm(-1) for A=K and Rb, respectively, SiH3- translations are between 95 and 160cm(-1), K+ translations are in the range 60-100cm(-1) and Rb+ translations in the range 50-70cm(-1). The red-shift of libration modes for A=Rb is associated with a 15-30% reduction of the libration force constants of SiH3- ions in -RbSiH3. This correlates with a lower temperature for the - order-disorder phase transition (278 vs 298K). Libration modes become significantly anharmonic with increasing temperature but are maintained up to at least 200K. The vibrational properties of ASiH(3) compare well to those of alkali metal borohydrides ABH(4) (A=Na-Cs).
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