A new family of metal borohydride guanidinate complexes: Synthesis, structures and hydrogen-storage properties

Journal Article · Sat Oct 15 00:00:00 EDT 2016 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/J.JSSC.2016.07.013· OSTI ID:22658041

Wu, Hui ^[1]; Zhou, Xiuquan; Rodriguez, Efrain E. ^[2]; Zhou, Wei; Udovic, Terrence J.; Yildirim, Taner ^[1]; Rush, John J. ^[1]

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1. NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899-6102 (United States)
2. Department of Chemistry & Biochemistry, University of Maryland, College Park, MD 20742-4454 (United States)

We report on a new class of complex hydrides: borohydride guanidinate complexes (MBH{sub 4}·nCN{sub 3}H{sub 5}, M=Li, Mg, and Ca). They can be prepared via facile solid-state synthesis routes. Their crystal structures were successfully determined using a combination of X-ray diffraction, first-principles calculations and neutron vibrational spectroscopy. Among these compounds, Mg(BH{sub 4}){sub 2}·6CN{sub 3}H{sub 5} is composed of large complex Mg[CN{sub 3}H{sub 5}]{sub 6}{sup 2+} cations and surrounding BH{sub 4}{sup -} ions, while Ca(BH{sub 4}){sub 2}·2CN{sub 3}H{sub 5} possesses layers of corner-sharing Ca[BH{sub 4}]{sub 4}(CN{sub 3}H{sub 5}){sub 2} octahedra. Our dehydrogenation results show that ≈10 wt% hydrogen can be released from MBH{sub 4}·nCN{sub 3}H{sub 5} (M=Li, Mg, and Ca) at moderate temperatures with minimal ammonia and diborane contamination thanks to the synergistic effect of C-N bonds from guanidine and hydridic H from borohydrides leading to a weakening of the N-H bonds, thus impeding ammonia gas liberation. Further tuning the dehydrogenation with different cation species indicates that Mg(BH{sub 4}){sub 2}·nCN{sub 3}H{sub 5} can exhibit the optimum properties with nearly thermally neutral dehydrogenation and very high purity hydrogen release. - Graphical abstract: A new family of complex hydrides: borohydride guanidinates, was developed with diverse crystal structures and remarkable hydrogen storage properties. - Highlights: • A new family of complex hydrides, borohydride guanidinate complexes, are synthesized. • Their diverse crystal structures are determined using combined characterizations. • These compounds can release ~10 wt% pure H{sub 2} at moderate temperatures. • Dehydrogenation thermodynamics and H{sub 2} purity can be tuned by varying cation species.

• OSTI ID: 22658041
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: Part 1 Vol. 242; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
BOROHYDRIDES
CATIONS
COMPLEXES
CRYSTAL STRUCTURE
DEHYDROGENATION
EXPERIMENTAL DATA
GUANIDINES
HYDROGEN STORAGE
IMPURITIES
METALS
NEUTRON SPECTROSCOPY
SYNTHESIS
X RADIATION
X-RAY DIFFRACTION