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首页> 外文期刊>Acta Crystallographica, Section B. Structural science, crystal engineering and materials >Fluxional seven-coordinated fluorido- and oxofluoridotantalates
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Fluxional seven-coordinated fluorido- and oxofluoridotantalates

机译：血型七配位氟化物和牛粪芴醇

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摘要

Seven-coordinated (NH_4)_2TaF_7, Rb_2TaF_7 and Rb_3TaOF_6 were synthesized in single-crystal form and their structures were determined. A monocapped trigonal prism (CTP) or a pentagonal bipyramid (PB) of the TaF_7~(2-) anion are stereochemically nonrigid and coexist in the first two compounds as a result of strong intraspheric dynamics. Upon cooling, tetragonal Rb_2TaF_7 undergoes a first-order phase transition at 145 K and the seven-coordinated polyhedron transforms into a regular CTP. The seven-coordinated polyhedron in (NH_4)_2TaF_7 approaches the PB configuration as the temperature decreases. Cubic elpasolite-like Rb_3TaOF_6 is characterized by the simultaneous two-state coexistence of TaOF_6~(3-) of the PB shape as rigidly reoriented and as fluxional. In the former case, the central atom is disordered over the octahedron in the unit cell, allowing the determination of the short Ta-O distance, whereas in the latter case, tantalum remains in the polyhedron center, resulting in synchronous Ta-O and Ta-F stretching vibrations appearing as the infrared band at 723 cm~(-1).
机译：以单晶形式合成七种协调（NH_4）_2TAF_7，RB_2TAF_7和RB_3TAOF_6，并确定它们的结构。 TAF_7〜（2-）阴离子的单次棱镜棱镜（CTP）或五角形双吡喃（Pb）是立体化学上的非脂肪和在前两种化合物中共存，其具有强大的骨干动力学。在冷却时，四方RB_2TAF_7经历145 k和七个协调的多面体变换成常规CTP的一阶相转变。在（NH_4）_2TAF_7中的七个协调多面体接近PB配置随着温度降低。立方体elpasogite的RB_3TAOF_6的特征在于，PB形状的TaOF_6〜（3-）的同时两态共存，与刚性重新定向和孔隙性。在前一种情况下，中央原子在单位细胞中的八面体中紊乱，允许确定短TA-O距离，而在后一种情况下，钽仍保留在多面体中心，导致同步TA-O和TA -f拉伸振动出现为723cm〜（-1）的红外带。

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