Exploring secondary bonding in p-block chemistry - an experimental study of [GeX 2 {o-C 6 H 4 (PMe 2 ) 2 }] using variable pressure single crystal X-ray diffraction
Exploring secondary bonding in p-block chemistry - an experimental study of [GeX 2 {o-C 6 H 4 (PMe 2 ) 2 }] using variable pressure single crystal X-ray diffraction
复制标题
探索 p 嵌段化学中的二次键合 - 使用变压单晶 X 射线衍射对 [GeX 2 {o-C 6 H 4 (PMe 2 ) 2 }] 进行实验研究
作者：
Allan D
二级键相互作用在控制所采用的整体结构中起主要作用。来自这些弱相互作用的低能量贡献使得结构预测非常困难，因此需要有助于理解不同类型的次级键合之间的相互作用的实验技术。对同源系列[GeX 2 {o-C6 H 4（PMe 2）2}]（X = Cl 1，Br 2，I 3）的变压单晶X射线衍射研究表明，探测结构构件层之间的不同界面，而不是传统的分子单元，提供了非常有价值的见解。1和3在压力增加时经历平滑压缩，而2在29和41 kbar之间的压力下发生相变。这与β角的突然变化（从111.33（2）°到92.24（8）°）有关。结构的后果是最明显的芳香族-芳香族层界面。在相变之下，存在边到面的C-H π π排列（如1），相邻环的平面之间的角度约为75°，而在相变之上，该界面已转变为偏移平行的面对面π-π堆积相互作用（如3）。GeX 2 → X2 Ge界面随着压力的增加而经历伴随的但更平滑的压缩。2在环境压力下也具有最高的空隙体积（11.9%），并且正如所预期的，相变导致具有更有效填充的结构。这是第一个涉及p-块配位复合物的研究，揭示了存在的不同形式的弱的二级（超分子）相互作用之间相互作用的微妙性和复杂性。结果表明，这种类型的实验研究可以提供有价值的额外信息，以帮助指导晶体结构预测的计算方法，一个重要的和非常具有挑战性的目标。
Secondary bonding interactions play a major role in governing the overall structures adopted. The low energy contributions from these weak interactions make structure prediction very difficult, hence there is a need for experimental techniques that contribute to understanding the interplay between different types of secondary bonding. Variable pressure single crystal X-ray diffraction studies on the homologous series, [GeX2{o-C6H4(PMe2)2}], X = Cl 1, Br 2, I 3, show that probing the different interfaces between layers of structural building blocks, rather than conventional molecular units, provides very valuable insights. 1 and 3 undergo a smooth compression as the pressure is increased, whereas a phase transition occurs for 2 at a pressure between 29 and 41 kbar. This is associated with an abrupt change in the β angle (from 111.33(2)° to 92.24(8)°). The structural consequences are most evident in the aromatic⋯aromatic layer interface. Below the phase transition there is an edge-to-face C–H⋯π arrangement (like 1), with the angle between the planes of adjacent rings of ~75°, whereas above the transition this interface has transformed to an offset-parallel face-to-face π–π stacking interaction (like 3). The GeX2⋯X2Ge interface undergoes a concomitant, but smoother compression with increasing pressure. 2 also has the highest void volume at ambient pressure (11.9%), and as expected the phase transition results in a structure with much more efficient packing. This, the first such study involving p-block coordination complexes, reveals the subtlety and complexity of the interplay between the different forms of weak, secondary (supramolecular) interactions present. The results indicate that this type of experimental study can provide valuable additional information to help guide crystal structure prediction by computational methods, an important and very challenging target.