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

Published

October 1, 2016

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 BH_{4- ions, while calcium borohydride guanidinate possesses layers of corner-sharing Ca[BH&d4}]₄(CN₃H₅)₂ octahedral with BH_4- ions in bridging and CN₃H₅ ligands in the trans positions. Strong dihydrogen bonding (NH^delta+...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

Pub Type

Journals

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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 October 27, 2025)