Na9Bi5Os3O24：一种独特的反磁性氧化物，具有明显的Jahn-Teller压缩八面体锇配位（VI）
Na9Bi5Os3O24: A Unique Diamagnetic Oxide Featuring a Pronouncedly Jahn-Teller Compressed Octahedral Coordination of Osmium(VI)
摘要：
Jahn-Teller定理是最流行和最严格的概念之一，适用于化学的所有领域。在开壳层过渡元素化学和物理学中，八面体络合物中的3d4、3d9和3d7（低自旋）构型作为特别说明性和可靠的例子，其中局部几何形状的显著变化（扭曲）与电子能量的大幅减少有关。然而，有一个持久的争论，关于八面体被发现只伸长的事实，（至少对电子来说）。在此背景下，标题化合物显示出两个显著的特征，（1）Os6+（d2）周围的氧原子八面体被急剧压缩，与标准JT预期相反，（2）由这种压缩引起的t2 g集的分裂是极端的，这样就产生了抗磁性的基态。我们看到的显然是一个Jahn-Teller畸变，导致了相应八面体的压缩，并作用于t2g轨道集。这两个问题都是前所未有的。值得注意的是，分裂成一个较低的dxy（拥有两个自旋相反的d电子）和两个较高的dxz和dyz轨道是如此之大，以至于第一次克服了t2g电子的洪德耦合。我们表明，这些影响是不是被迫的结构挫折，结构提供了足够的空间，为Os的顶端氧原子移动到一个标准的距离。相反，当地的电子效应似乎是负责任的。这些发现的相关性是深远的，因为它们提供了在定义开壳层电子系统的基态的扰动层次的见解。这里研究的系统，提供了更多的结构和组成的自由度，这样的配置可以形成，使Os6+采取其明显真正的抗磁基态。
英文摘要：
The Jahn-Teller theorem constitutes one of the most popular and stringent concepts, applicable to all fields of chemistry. In open shell transition elements chemistry and physics, 3d4, 3d9, and 3d7(low-spin) configurations in octahedral complexes serve as particular illustrative and firm examples, where a striking change (distortion) in local geometry is associated to a substantial reduction of electronic energy. However, there has been a lasting debate, about the fact that the octahedra are found to exclusively elongate, (at least for eg electrons). Against this background, the title compound displays two marked features, (1) the octahedron of oxygen atoms around Os6+ (d2) is drastically compressed, in contrast to the standard JT expectations, and (2) the splitting of the t2g set induced by this compression is extreme, such that a diamagnetic ground state results. What we see is obviously a Jahn-Teller distortion resulting in a compression of the respective octahedron and acting on the t2g set of orbitals. Both these issues are unprecedented. Noteworthy, the splitting into a lower dxy (hosting two d electrons with opposite spin) and two higher dxz and dyz orbitals is so large that for the first time ever the Hund's coupling for t2g electrons is overcome. We show that these effects are not forced by structural frustration, the structure offers sufficient space for Os to shift the apical oxygen atoms to a standard distance. Local electronic effects appear to be responsible, instead. The relevance of these findings is far reaching, since they provide insights in the hierarchy of perturbations defining ground states of open shell electronic systems. The system studied here, offers substantially more structural and compositional degrees of freedom, such that a configuration could form that enables Os6+ to adopt its apparently genuine diamagnetic ground state.
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