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A New Family of Metal Borohydride Guanidinate Complexes: Synthesis, Structures and Hydrogen-Storage Properties

Published

Author(s)

Hui Wu, Xiuquan Zhou, Efrain E. Rodriguez, Wei Zhou, Terrence J. Udovic, Taner Yildirim, John J. Rush

Abstract

We report a new class of high-hydrogen-content inorganic-organic hybrid complex hydrides: borohydride guanidinate complexes (MBH4•nCN3H5, 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 synthesized, magnesium borohydride guanidinate is composed of large complex Mg[CN3H5]62+ cations and surrounding BH4- ions, while calcium borohydride guanidinate possesses layers of corner-sharing Ca[BH&d4]4(CN3H5)2 octahedral with BH4- ions in bridging and CN3H5 ligands in the trans positions. Strong dihydrogen bonding (NHdelta+...uδ-HB^) is established in these compounds. Our dehydrogenation results show that {approximately equal}10 mass% hydrogen can be released from MBH4•nCN3H5 (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 magnesium borohydride guanidinate can exhibit the optimum properties with nearly thermally neutral dehydrogenation and very high purity hydrogen release.
Citation
Journal of Solid State Chemistry
Volume
242
Issue
1

Keywords

Complex hydride, crystal structure, borohydride, neutron vibrational spectroscopy

Citation

Wu, H. , Zhou, X. , , E. , Zhou, W. , , T. , Yildirim, T. and Kasianowicz, J. (2016), A New Family of Metal Borohydride Guanidinate Complexes: Synthesis, Structures and Hydrogen-Storage Properties, Journal of Solid State Chemistry, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=920475 (Accessed February 26, 2024)
Created October 1, 2016, Updated October 27, 2017