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Transition Metal Hydride Complexes and Hydrogenated Gallium Clusters: Synthesis and Structural Properties
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry (MMK), Stockholm University , 2013. , 64 p.
Keyword [en]
Metal hydrides, Solid state Synthesis, X-ray diffraction, Neutron Scattering
National Category
Inorganic Chemistry
Research subject
Structural Chemistry
Identifiers
URN: urn:nbn:se:su:diva-89760ISBN: 978-91-7447-711-5 (print)OAI: oai:DiVA.org:su-89760DiVA: diva2:620063
Public defence
2013-06-05, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time for the doctoral defence the following papers were unpublished and had a status as follows: Paper 1: Manuscript; Paper 2: Accepted; Paper 5: Manuscript

Available from: 2013-05-14 Created: 2013-05-07 Last updated: 2013-05-07Bibliographically approved
List of papers
1. 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
Open this publication in new window or tab >>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
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

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.

National Category
Materials Chemistry
Research subject
Structural Chemistry
Identifiers
urn:nbn:se:su:diva-89754 (URN)
Funder
The Swedish Energy Agency
Available from: 2013-05-07 Created: 2013-05-07 Last updated: 2013-05-07
2. Structural characterization of Sr4Mg4H4[CoH5]3 shows the importance of support from polarizingcounter ions to 3d transition metal hydrido complexes
Open this publication in new window or tab >>Structural characterization of Sr4Mg4H4[CoH5]3 shows the importance of support from polarizingcounter ions to 3d transition metal hydrido complexes
(English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669Article in journal (Refereed) Accepted
Abstract [en]

The structure of the title compound was refined from neutronpowder diffraction data in the cubic space group P-43m (215). The unitcell contains one formula unit with 3 structurally equivalent [Co(I)H5]4-complexes as well as 4 interstitial hydride (H-) ions. The presence ofthe larger and less polarizing Sr2+ ions weakens the bond in thecomplexes and probably also the stability of the structure. Attempts tosynthesize the corresponding Ba analogue failed in contrast to usingsmaller and more polarizing Ca2+ and Yb2+ counterions.

National Category
Inorganic Chemistry
Research subject
Structural Chemistry
Identifiers
urn:nbn:se:su:diva-89755 (URN)
Funder
The Swedish Energy Agency
Available from: 2013-05-07 Created: 2013-05-07 Last updated: 2017-12-06
3. Two New Cluster Ions, Ga[GaH(3)](4)(5-) with a Neopentane Structure in Rb(8)Ga(5)H(15) and [GaH(2)](n)(n-) with a Polyethylene Structure in Rb(n)(GaH(2))(n), Represent a New Class of Compounds with Direct Ga-Ga Bonds Mimicking Common Hydrocarbons
Open this publication in new window or tab >>Two New Cluster Ions, Ga[GaH(3)](4)(5-) with a Neopentane Structure in Rb(8)Ga(5)H(15) and [GaH(2)](n)(n-) with a Polyethylene Structure in Rb(n)(GaH(2))(n), Represent a New Class of Compounds with Direct Ga-Ga Bonds Mimicking Common Hydrocarbons
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2011 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 133, no 37, 14574-14577 p.Article in journal (Refereed) Published
Abstract [en]

The first examples of a new class of gallium hydride clusters with direct Ga-Ga bonds and common hydrocarbon structures are reported. Neutron powder diffraction was used to find a Ga[GaH(3)](4)(5-) cluster ion with a neopentane structure in a novel cubic structure type of Rb(8)Ga(5)H(15). Another cluster ion with a polyethylene structure, [GaH(2)](n)(n-), was found in a second novel (RbGaH(2))(n) hydride. These hydrocarbon-like clusters in gallium hydride materials have significant implications for the discovery of hydrides for hydrogen storage as well as for interesting electronic properties.

National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-66530 (URN)10.1021/ja2067687 (DOI)000295148100028 ()
Note
authorCount :5Available from: 2011-12-27 Created: 2011-12-20 Last updated: 2017-12-08
Bibliographically approved
4. Varying the Alkali-Metal Radii in (KxRb1−x)n[GaH2]n (0 ≤ x ≤ 1)Reorients a Stable Polyethylene-Structured [GaH2]nn− Anionic Chain
Open this publication in new window or tab >>Varying the Alkali-Metal Radii in (KxRb1−x)n[GaH2]n (0 ≤ x ≤ 1)Reorients a Stable Polyethylene-Structured [GaH2]nn− Anionic Chain
2013 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 52, no 9, 4771-4773 p.Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Inorganic Chemistry
Research subject
Structural Chemistry
Identifiers
urn:nbn:se:su:diva-89752 (URN)10.1021/ic400224a (DOI)000318669400009 ()
Funder
Swedish Energy Agency
Note

AuthorCount: 3;

Available from: 2013-05-07 Created: 2013-05-07 Last updated: 2017-12-06Bibliographically approved
5. Cs10H[Ga3H8]3: A Hydrogenous Zintl Phase Containing Propane-Like Polyanions [Ga3H8]3- and Interstitial Hydrogen
Open this publication in new window or tab >>Cs10H[Ga3H8]3: A Hydrogenous Zintl Phase Containing Propane-Like Polyanions [Ga3H8]3- and Interstitial Hydrogen
2013 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 52, no 12, 7125-7129 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Metal hydrides, Polyanionic, X-ray powder diffraction, Neutron Powder diffraction, Solid state synthesis
National Category
Materials Chemistry
Research subject
Structural Chemistry
Identifiers
urn:nbn:se:su:diva-89753 (URN)10.1021/ic400714e (DOI)000320689200042 ()
Available from: 2013-05-07 Created: 2013-05-07 Last updated: 2017-12-06Bibliographically approved

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