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Polyanionic gallium hydrides from AlB2-type precursors AeGaE (Ae = Ca, Sr, Ba; E = Si, Ge, Sn)
Michael J Evans1, Gregory P Holland, Francisco J Garcia-Garcia
1Department of Chemistry and Biochemistry, Arizona State University, P.O. Box 871604, Tempe, Arizona 85287-1604, USA.
Journal of the American Chemical Society
|August 14, 2008
Summary
New quaternary hydrides like SrGaGeH were synthesized from intermetallic compounds. These materials exhibit a reversible metal-nonmetal transition and feature a unique 2D polyanion structure, with potential applications in materials science.
Area of Science:
- Materials Science
- Solid State Chemistry
- Inorganic Chemistry
Background:
- Investigated hydrogenation behavior of alkaline earth metal (Ae) - gallium (Ga) - pnictogen (E) intermetallic compounds (Ae = Ca, Sr, Ba; E = Si, Ge, Sn).
- Precursor phases AeGaE exhibit metallic properties and crystallize in the AlB2 structure type or its variants.
Purpose of the Study:
- Synthesize and structurally characterize novel quaternary hydrides (deuterides) of the formula AeGaEH(D).
- Explore the electronic properties and hydrogen storage characteristics of these new main group metal/semimetal hydrides.
Main Methods:
- Synthesis via hydrogenation of intermetallic precursors.
- Structural characterization using powder X-ray diffraction, neutron diffraction, and solid-state (1)H NMR spectroscopy.
- Electronic property analysis through band gap determination.
Main Results:
- Successfully obtained SrGaGeH(D), BaGaSiH(D), BaGaGeH(D), and BaGaSnH(D).
- These hydrides crystallize in the trigonal SrAlSiH structure type, featuring a 2D [GaEH](2-) polyanion.
- Exhibited small band gaps (0.1-0.6 eV), indicating a metal-nonmetal transition upon hydrogenation.
- Reversible metal-nonmetal transition observed for SrGaGe, BaGaSi, and BaGaGe; BaGaSnH showed partial decomposition upon hydrogen release.
- High hydrogen desorption temperatures (>400 °C).
Conclusions:
- The synthesized quaternary hydrides represent a new class of main group metal/semimetal compounds.
- The [GaEH](2-) polyanion structure and resulting electronic properties are key features.
- Reversibility of the metal-nonmetal transition suggests potential for hydrogen-related applications.
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