一个由德国马普所Martin Jansen教授带领的国际合作小组近日发现了一种受姜-泰勒（Jahn-Teller）效应高度压缩的八面体配位锇(VI)抗磁性氧化物Na₉Bi₅Os₃O₂₄。相关论文于2021年4月27日发表在《德国应用化学》杂志上。

姜-泰勒效应是化学领域最基本，最严格的概念之一。在过渡元素化学中，八面体配合物中的3d⁴、3d⁹和3d⁷构象的姜-泰勒效应尤为显著，其中局部几何构型的扭曲与电子能量减少有关。然而，关于八面体只会被拉长这一事实却一直存在着持久的争论。与之相反，研究人员发现，对于Na₉Bi₅Os₃O₂₄， Os⁶⁺(5d²)周围的八面体被严重压缩，这种压缩引起的5d轨道的t_2g组发生的裂分非常极端，以至于导致出现了一种抗磁性的基态，这两种情况都是非常罕见的。

进一步研究表明，一个较低的d_xy轨道（包含两个自旋相反的d电子）和两个较高的d_xz轨道和d_yz轨道之间的裂分是如此之大，以致于克服了t_2g电子按照洪特规则偶合。该效应并非受结构约束条件的强迫所致，因为该结构为Os提供了足够的空间将顶氧原子移动一个常规的距离。

研究人员表示，这些发现有着深远的意义，因为它们为定义开壳层电子系统基态的扰动层次提供了一些洞见。

附：英文原文

Title: Na9Bi5Os3O24: A  Diamagnetic Oxide Featuring a Pronouncedly Jahn‐Teller Compressed Octahedral Coordination of Osmium(VI)

Author: Martin Jansen, Gohil S. Thakur, Hans Reuter, Alexey V. Ushakov, Gianpiero Gallo, Jü, Robert E. Dinnebier, Sergey V. Streltsov, Daniel I. Khomskii

Issue&Volume: 2021-04-27

Abstract: The Jahn‐Teller (JT) theorem constitutes one of the most fundamental and stringent concepts in chemistry. In transition elements chemistry, the 3  d  4  , 3  d  9  , and 3  d  7  configurations in octahedral complexes are particularly illustrative, where a distortion in local geometry is associated to a reduction of electronic energy. However, there has been a lasting debate about the fact that the octahedra are found to exclusively elongate. In contrast, for Na  9  Bi  5  Os  3  O  24  , the octahedron around Os  6+  (5  d  2  ) is heavily compressed, and the splitting of the  t  2g  set of 5  d  orbitals induced by this compression is extreme, such that a diamagnetic ground state results. Both these issues are extremely rare. The splitting into a lower  d  xy  (hosting two  d  electrons with opposite spin) and two higher  d  xz  and  d  yz  orbitals is so large that the Hund′s coupling for  t  2g  electrons is overcome. These effects are not forced by structural constraints, the structure offers sufficient space for osmium to shift the apical oxygen atoms to a standard distance. 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.

DOI: 10.1002/anie.202103295

Source: https://onlinelibrary.wiley.com/doi/10.1002/anie.202103295