Grinderslev Jakob B, Jepsen Lars H, Lee Young-Su, Møller Kasper T, Cho Young Whan, Černý Radovan, Jensen Torben R
Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, Langelandsgade 140, DK-8000 Aarhus C, Denmark.
Center for Energy Materials Research, Korea Institute of Science and Technology, Seoul 02792, Republic of Korea.
Inorg Chem. 2020 Sep 8;59(17):12733-12747. doi: 10.1021/acs.inorgchem.0c01797. Epub 2020 Aug 17.
Metal borohydrides are a fascinating and continuously expanding class of materials, showing promising applications within many different fields of research. This study presents 17 derivatives of the hydrogen-rich ammonium borohydride, NHBH, which all exhibit high gravimetric hydrogen densities (>9.2 wt % of H). A detailed insight into the crystal structures combining X-ray diffraction and density functional theory calculations exposes an intriguing structural variety ranging from three-dimensional (3D) frameworks, 2D-layered, and 1D-chainlike structures to structures built from isolated complex anions, in all cases containing NH countercations. Dihydrogen interactions between complex NH and BH ions contribute to the structural diversity and flexibility, while inducing an inherent instability facilitating hydrogen release. The thermal stability of the ammonium metal borohydrides, as a function of a range of structural properties, is analyzed in detail. The Pauling electronegativity of the metal, the structural dimensionality, the dihydrogen bond length, the relative amount of NH to BH, and the nearest coordination sphere of NH are among the most important factors. Hydrogen release usually occurs in three steps, involving new intermediate compounds, observed as crystalline, polymeric, and amorphous materials. This research provides new opportunities for the design and tailoring of novel functional materials with interesting properties.
金属硼氢化物是一类引人入胜且不断发展的材料，在许多不同的研究领域都展现出了广阔的应用前景。本研究展示了17种富氢硼氢化铵（NH₄BH₄）的衍生物，它们均表现出较高的氢重量密度（>9.2 wt% H）。结合X射线衍射和密度泛函理论计算对晶体结构进行的详细研究揭示了一种有趣的结构多样性，从三维（3D）框架结构、二维层状结构、一维链状结构到由孤立的复合阴离子构成的结构，所有情况下都含有NH₄⁺抗衡阳离子。复合的NH₄⁺和BH₄⁻离子之间的双氢键相互作用有助于结构的多样性和灵活性，同时引发内在的不稳定性，促进氢的释放。详细分析了铵基金属硼氢化物的热稳定性与其一系列结构性质之间的关系。金属的鲍林电负性、结构维度、双氢键长度、NH₄⁺与BH₄⁻的相对含量以及NH₄⁺的最近配位球是其中最重要的因素。氢的释放通常分三步进行，涉及新的中间化合物，表现为晶体、聚合物和无定形材料。这项研究为设计和定制具有有趣性质的新型功能材料提供了新的机会。
