Evidence of Intermediate Hydrogen States in the Formation of a Complex Hydride

Toyoto Sato; Anibal J. Ramirez-Cuesta; Luke L. Daemen; Yongqiang Cheng; Shin Ichi Orimo

doi:10.1021/acs.inorgchem.7b02834

Evidence of Intermediate Hydrogen States in the Formation of a Complex Hydride

Toyoto Sato, Anibal J. Ramirez-Cuesta, Luke L. Daemen, Yongqiang Cheng, Shin Ichi Orimo

Research output: Contribution to journal › Article › peer-review

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Abstract

A complex hydride (LaMg₂NiH₇) composed of La³⁺, two Mg²⁺, [NiH₄]^4- with a covalently bonded hydrogen, and three H^- was formed from an intermetallic LaMg₂Ni via an intermediate phase (LaMg₂NiH_4.6) composed of La, Mg, NiH₂, NiH₃ units, and H atoms at tetrahedral sites. The NiH₂ and NiH₃ units in LaMg₂NiH_4.6 were reported as precursors for [NiH₄]^4- in LaMg₂NiH₇ [ Miwa et al. J. Phys. Chem. C 2016, 120, 5926-5931 ]. To further understand the hydrogen states in the precursors (the NiH₂ and NiH₃ units) and H atoms at the tetrahedral sites in the intermediate phase, LaMg₂NiH_4.6, we observed the hydrogen vibrations in LaMg₂NiH_4.6 and LaMg₂NiH₇ by using inelastic neutron scattering. A comparison of the hydrogen vibrations of the NiH₂ and NiH₃ units with that of [NiH₄]^4- shows that the librational modes of the NiH₂ and NiH₃ units were nonexistent; librational modes are characteristic modes for complex anions, such as [NiH₄]^4-. Furthermore, the hydrogen vibrations for the H atoms in the tetrahedral sites showed a narrower wavenumber range than that for H^- and a wider range than that for typical interstitial hydrogen. The results indicated the presence of intermediate hydrogen states before the formation of [NiH₄]^4- and H^-.

Original language	English
Pages (from-to)	867-872
Number of pages	6
Journal	Inorganic Chemistry
Volume	57
Issue number	2
DOIs	https://doi.org/10.1021/acs.inorgchem.7b02834
State	Published - Jan 16 2018
Externally published	Yes

Funding

We are grateful for the technical support from Ms. H. Ohmiya and Ms. N. Warifune. This research was supported by the Japan Society for the Promotion of Science (JSPS) Grants-in-Aid for Scientific Research (KAKENHI), grant nos. 16K06766 and 25220911, from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan, and the Collaborative Research Center on Energy Materials in the Institute for Materials Research (E-IMR), Tohoku University. This research benefited from the use of the VISION beamline (IPTS-16527) at the Spallation Neutron Source of Oak Ridge National Laboratory (ORNL), supported by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy, under contract no. DE-AC0500OR22725. Computational resources were made available through the VirtuES and ICE-MAN projects, funded by the Laboratory Directed Research and Development at ORNL.

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title = "Evidence of Intermediate Hydrogen States in the Formation of a Complex Hydride",

abstract = "A complex hydride (LaMg2NiH7) composed of La3+, two Mg2+, [NiH4]4- with a covalently bonded hydrogen, and three H- was formed from an intermetallic LaMg2Ni via an intermediate phase (LaMg2NiH4.6) composed of La, Mg, NiH2, NiH3 units, and H atoms at tetrahedral sites. The NiH2 and NiH3 units in LaMg2NiH4.6 were reported as precursors for [NiH4]4- in LaMg2NiH7 [ Miwa et al. J. Phys. Chem. C 2016, 120, 5926-5931 ]. To further understand the hydrogen states in the precursors (the NiH2 and NiH3 units) and H atoms at the tetrahedral sites in the intermediate phase, LaMg2NiH4.6, we observed the hydrogen vibrations in LaMg2NiH4.6 and LaMg2NiH7 by using inelastic neutron scattering. A comparison of the hydrogen vibrations of the NiH2 and NiH3 units with that of [NiH4]4- shows that the librational modes of the NiH2 and NiH3 units were nonexistent; librational modes are characteristic modes for complex anions, such as [NiH4]4-. Furthermore, the hydrogen vibrations for the H atoms in the tetrahedral sites showed a narrower wavenumber range than that for H- and a wider range than that for typical interstitial hydrogen. The results indicated the presence of intermediate hydrogen states before the formation of [NiH4]4- and H-.",

author = "Toyoto Sato and Ramirez-Cuesta, {Anibal J.} and Daemen, {Luke L.} and Yongqiang Cheng and Orimo, {Shin Ichi}",

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AU - Orimo, Shin Ichi

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N2 - A complex hydride (LaMg2NiH7) composed of La3+, two Mg2+, [NiH4]4- with a covalently bonded hydrogen, and three H- was formed from an intermetallic LaMg2Ni via an intermediate phase (LaMg2NiH4.6) composed of La, Mg, NiH2, NiH3 units, and H atoms at tetrahedral sites. The NiH2 and NiH3 units in LaMg2NiH4.6 were reported as precursors for [NiH4]4- in LaMg2NiH7 [ Miwa et al. J. Phys. Chem. C 2016, 120, 5926-5931 ]. To further understand the hydrogen states in the precursors (the NiH2 and NiH3 units) and H atoms at the tetrahedral sites in the intermediate phase, LaMg2NiH4.6, we observed the hydrogen vibrations in LaMg2NiH4.6 and LaMg2NiH7 by using inelastic neutron scattering. A comparison of the hydrogen vibrations of the NiH2 and NiH3 units with that of [NiH4]4- shows that the librational modes of the NiH2 and NiH3 units were nonexistent; librational modes are characteristic modes for complex anions, such as [NiH4]4-. Furthermore, the hydrogen vibrations for the H atoms in the tetrahedral sites showed a narrower wavenumber range than that for H- and a wider range than that for typical interstitial hydrogen. The results indicated the presence of intermediate hydrogen states before the formation of [NiH4]4- and H-.

AB - A complex hydride (LaMg2NiH7) composed of La3+, two Mg2+, [NiH4]4- with a covalently bonded hydrogen, and three H- was formed from an intermetallic LaMg2Ni via an intermediate phase (LaMg2NiH4.6) composed of La, Mg, NiH2, NiH3 units, and H atoms at tetrahedral sites. The NiH2 and NiH3 units in LaMg2NiH4.6 were reported as precursors for [NiH4]4- in LaMg2NiH7 [ Miwa et al. J. Phys. Chem. C 2016, 120, 5926-5931 ]. To further understand the hydrogen states in the precursors (the NiH2 and NiH3 units) and H atoms at the tetrahedral sites in the intermediate phase, LaMg2NiH4.6, we observed the hydrogen vibrations in LaMg2NiH4.6 and LaMg2NiH7 by using inelastic neutron scattering. A comparison of the hydrogen vibrations of the NiH2 and NiH3 units with that of [NiH4]4- shows that the librational modes of the NiH2 and NiH3 units were nonexistent; librational modes are characteristic modes for complex anions, such as [NiH4]4-. Furthermore, the hydrogen vibrations for the H atoms in the tetrahedral sites showed a narrower wavenumber range than that for H- and a wider range than that for typical interstitial hydrogen. The results indicated the presence of intermediate hydrogen states before the formation of [NiH4]4- and H-.

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Evidence of Intermediate Hydrogen States in the Formation of a Complex Hydride

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