Hydrogen absorption in transition metal suicides: La3Pd 5Si-hydrogen system
(2008) Inorganic Chemistry — Vol. 47, n° 14, p. 6303-6313 (2008)
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- Abstract
- Pressure-composition isotherm measurements show that the ternary lanthanum palladium suicide phase La3Pd5Si absorbs reversibly up to 5 hydrogen atoms per formula unit at 550 K and 14 bar hydrogen pressure. In-situ synchrotron and neutron powder diffraction reveals three phases, an α-phase having the limiting composition La3Pd 5SiD∼1.6 at low deuterium pressure (at up to 9.5 bar D2 and 550 K), a β-phase La3Pd5SiD ∼2.30-4 at intermediate deuterium pressure (<9.5 bar D 2 and 550 K), and a relatively unstable γ-phase La 3Pd5SiD∼5 at high deuterium pressure (obtained at 75 bar D2 and 293 K). While the α and β phases retain the symmetry of the H-free La3Pd5Si (space group Imma), the γ-phase undergoes a symmetry lowering (a γ-aβ, bγ-3bβ and cγ-cβ, Vγ-3V β, space group Pmnb). The structure of the α-phase contains isolated [Pd-D-Pd] fragments, which are joined into polymeric (-Pd-D-Pd-)n zig-zag chains in the β-phase. In the γ-phase some D sites depopulate, while new D sites are occupied, thus leading to a partial interruption of the zig-zag chains and the formation of isolated [D-Pd-D-Pd] and [D-Pd-D-Pd-D] fragments. This unexpected behavior can be attributed to the onset of repulsive Si-D and D-D interactions (Si-D > 3.0 Å, D-D > 2.1 Å) that divide the structure into Si-poor slabs that absorb hydrogen and Si-rich slabs that do not. The competition between silicon and deuterium which act as a transition metal ligand is further underlined by the fact that Pd atoms having one Si ligand are capable of forming Pd-D bonds, whereas Pd atoms having two Si ligands are not. © 2008 American Chemical Society.
- Affiliations
ESRF, Grenoble (France) Chimie
Citations
Tokaychuk, Y. O., Filinchuk, Y., Sheptyakov, D. V., & Yvon, K. (2008). Hydrogen absorption in transition metal suicides: La3Pd 5Si-hydrogen system. Inorganic Chemistry, 47(14), 6303-6313. https://doi.org/10.1021/ic800382x (Original work published 2008)