Trends in Syntheses, Structures, and Properties for Three Series of Ammine Rare-Earth Metal Borohydrides M(BH4)3·nNH3 (M = Y, Gd, and Dy)

Jepsen, Lars H.; Ley, Morten B.; Cerny, Radovan; Lee, Young-Su; Cho, Young Whan; Ravnsbæk, Dorthe; Besenbacher, Flemming; Skibsted, Jørgen; Jensen, Torben R.

doi:10.1021/acs.inorgchem.5b00951

Scientific article

English

Trends in Syntheses, Structures, and Properties for Three Series of Ammine Rare-Earth Metal Borohydrides M(BH₄)₃·nNH₃ (M = Y, Gd, and Dy)

Contributors

Jepsen, Lars H.; Ley, Morten B.; Cerny, Radovan; Lee, Young-Su; Cho, Young Whan; Ravnsbæk, Dorthe; Besenbacher, Flemming; Skibsted, Jørgen; Jensen, Torben R.

Published in

Inorganic chemistry, vol. 54, no. 15, p. 7402-7414

Publication date

2015

Abstract

Fourteen solvent- and halide-free ammine rare-earth metal borohydrides M(BH4)3·nNH3, M = Y, Gd, Dy, n = 7, 6, 5, 4, 2, and 1, have been synthesized by a new approach, and their structures as well as chemical and physical properties are characterized. Extensive series of coordination complexes with systematic variation in the number of ligands are presented, as prepared by combined mechanochemistry, solvent-based methods, solid–gas reactions, and thermal treatment. This new synthesis approach may have a significant impact within inorganic coordination chemistry. Halide-free metal borohydrides have been synthesized by solvent-based metathesis reactions of LiBH4 and MCl3 (3:1), followed by reactions of M(BH4)3 with an excess of NH3 gas, yielding M(BH4)3·7NH3 (M = Y, Gd, and Dy). Crystal structure models for M(BH4)3·nNH3 are derived from a combination of powder X-ray diffraction (PXD), 11B magic-angle spinning NMR, and density functional theory (DFT) calculations. The structures vary from two-dimensional layers (n = 1), one-dimensional chains (n = 2), molecular compounds (n = 4 and 5), to contain complex ions (n = 6 and 7). NH3 coordinates to the metal in all compounds, while BH4– has a flexible coordination, i.e., either as a terminal or bridging ligand or as a counterion. M(BH4)3·7NH3 releases ammonia stepwise by thermal treatment producing M(BH4)3·nNH3 (6, 5, and 4), whereas hydrogen is released for n ≤ 4. Detailed analysis of the dihydrogen bonds reveals new insight about the hydrogen elimination mechanism, which contradicts current hypotheses. Overall, the present work provides new general knowledge toward rational materials design and preparation along with limitations of PXD and DFT for analysis of structures with a significant degree of dynamics in the structures.

Keywords

Hydrogen storage
Metal borohydride
Powder diffraction

UNIGE affiliation entities

Faculté des sciences / Section de physique / Département de physique de la matière quantique

UNIGE research groups

Groupe Cerny

Funding

Swiss National Science Foundation - Polymetallic borohydrides for hydrogen storage and lithium batteries: crystal engineering. [149218]

Citation (ISO format)

JEPSEN, Lars H. et al. Trends in Syntheses, Structures, and Properties for Three Series of Ammine Rare-Earth Metal Borohydrides M(BH₄)₃·nNH₃ (M = Y, Gd, and Dy). In: Inorganic chemistry, 2015, vol. 54, n° 15, p. 7402–7414. doi: 10.1021/acs.inorgchem.5b00951

Article (Published version)

Identifiers

PID : unige:77573
DOI : 10.1021/acs.inorgchem.5b00951

Journal ISSN

0020-1669

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18/11/2015 16:20:00

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