Trends in Synthesis, Crystal Structure, and Thermal and Magnetic Properties of Rare-Earth Metal Borohydrides
Trends in Synthesis, Crystal Structure, and Thermal and Magnetic Properties of Rare-Earth Metal Borohydrides
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DOI：
10.1021/acs.inorgchem.8b03258
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发表时间：
2019-05-06
影响因子：
4.6
通讯作者：
Jensen, Torben R.
中科院分区：
文献类型：
--
作者：
Grinderslev, Jakob B.;Moller, Kasper T.;Jensen, Torben R.
介绍了全系列无卤化物稀土 (RE) 金属硼氢化物的合成、晶体结构以及热性能和磁性能。新的合成方法提供了高产率和高纯度的产品。报道了十五种新的金属硼氢化物结构。比较和讨论了整个系列 RE(BH4)(x) 的晶体结构、热行为和磁性能的趋势。 RE(BH4)(x) 具有非常丰富的晶体化学性质，具体取决于稀土离子的氧化态和离子大小。由于镧系收缩，随着原子序数的增加，RE3+-离子的体积显着减小，这与α-和β-RE(BH4)(3)多晶型物以及溶剂化复合物α-RE(BH4)(3)中心点S(CH3)(2)的晶胞体积线性相关。热分析表明，除 Lu(BH4)(3) 外，所有 RE(BH4)(3) 在 247 至 277 ℃ 的温度范围内均呈现一步分解路径，Lu(BH4)(3) 遵循三步分解路径。相比之下，由于稀土离子的电荷密度较低，RE(BH4)(2) 在 306 至 390 摄氏度的较高温度下分解。 RE(BH4)(3) 随着鲍林电负性的增加而表现出稳定性的增加，这与其他主族和过渡金属硼氢化物相矛盾。大多数化合物在低至 3 K 时都遵循居里-维斯顺磁行为，具有弱反铁磁相互作用和与孤立 4f 离子一致的磁矩。由于晶体场效应引起的低位激发态，一些 RE(BH4)(x) 显示出不同程度的温度依赖性磁矩。此外，在 Gd(BH4)(3) 中观察到弱反铁磁有序性，表明通过硼氢化物基团进行了超交换。
Synthesis, crystal structures, and thermal and magnetic properties of the complete series of halide-free rare-earth (RE) metal borohydrides are presented. A new synthesis method provides high yield and high purity products. Fifteen new metal borohydride structures are reported. The trends in crystal structures, thermal behavior, and magnetic properties for the entire series of RE(BH4)(x) are compared and discussed. The RE(BH4)(x) possess a very rich crystal chemistry, dependent on the oxidation state and the ionic size of the rare-earth ion. Due to the lanthanide contraction, there is a significant decrease in the volume of the RE3+-ion with increasing atomic number, which correlates linearly with the unit cell volume of the alpha- and beta-RE(BH4)(3) polymorphs and the solvated complexes alpha-RE(BH4)(3) center dot S(CH3)(2). The thermal analysis reveals a one-step decomposition pathway in the temperature range from 247 to 277 degrees C for all RE(BH4)(3) except Lu(BH4)(3), which follows a three-step decomposition pathway. In contrast, the RE(BH4)(2) decompose at higher temperatures in the range 306 to 390 degrees C due to lower charge density on the rare-earth ion. The RE(BH4)(3) show increasing stability with increasing Pauling electronegativity, which contradicts other main group and transition metal borohydrides. The majority of the compounds follow Curie-Weiss paramagnetic behavior down to 3 K with weak antiferromagnetic interactions and magnetic moments in accord with those of isolated 4f ions. Some of the RE(BH4)(x) display varying degrees of temperature-dependent magnetic moments due to low-lying excited stated induced by crystal field effects. Additionally, a weak antiferromagnetic ordering is observed in Gd(BH4)(3), indicating superexchange through a borohydride group.