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

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• 作者：Lars H. Jepsen ; Morten B. Ley ; Radovan 膶ern媒 ; Young-Su Lee ; Young Whan Cho ; Dorthe Ravnsb忙k ; Flemming Besenbacher ; J酶rgen Skibsted ; Torben R. Jensen
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：August 3, 2015
• 年：2015
• 卷：54
• 期：15
• 页码：7402-7414
• 全文大小：755K
• ISSN：1520-510X

文摘

Fourteen solvent- and halide-free ammine rare-earth metal borohydrides M(BH₄)₃路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鈥揼as 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路7NH₃ (M = Y, Gd, and Dy). Crystal structure models for M(BH₄)₃路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^{鈥?/sup> has a flexible coordination, i.e., either as a terminal or bridging ligand or as a counterion. M(BH₄)₃路7NH₃ releases ammonia stepwise by thermal treatment producing M(BH₄)₃路nNH₃ (6, 5, and 4), whereas hydrogen is released for n 鈮?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.}