Experimental characterization of the chemical bonds in boron allotropes and boron-rich compounds

尽管多年来进行了深入的研究，但涉及硼原子的化学键仍不清楚。例如，不知道硼的哪种同素异形体在环境条件下是稳定形式。该项目旨在通过单晶X射线衍射对硼的同素异形体（如β-B106和α-四氢硼）和富硼固体（如B13 C2和B50 C2）进行实验表征。多极（MP）模型的结构改进和数据分析，根据最大熵方法（MEM）将产生电子密度图，反映了价电子的空间分布的全部细节。根据Bader的分子中原子（AIM）理论对电子密度进行定量拓扑分析，将通过键临界点（BCP）、环临界点（RCP）和键路径对不同类型的化学相互作用进行分类。除了原子对之间正常的两电子两中心（2 e2 c）键，我们预计硼原子的缺电子性质将导致多中心键，两电子三中心（2 e3 c）键和各种类型的一电子两中心（1 e2 c）键。目标是发展一个广义的描述化学键，涉及硼原子在不同的同素异形体和化合物。

Chemical bonding involving boron atoms is not understood, despite intensive research over many years. For example, it is not known, which allotrope of boron is the stable form at ambient conditions. This project aims at an experimental characterization by single-crystal X-ray diffraction of allotropes of boron, like beta-B106 und alpha-tetragonal boron, and boron-rich solids, like B13C2 and B50C2. Structure refinements of the multipole (MP) model and data analysis according to the Maximum Entropy Method (MEM) will produce electron-density maps that reflect the spatial distribution of the valence electrons in full detail. A quantitative topological analysis of electron densities according to Bader's Atoms-in-Molecules (AIM) theory will classify the different kinds of chemical interactions through bond critical points (BCP), ring critical points (RCP) and bond paths. Next to normal two-electron-two-center (2e2c) bonds between pairs of atoms, we expect that the electron deficient nature of the boron atom will lead to polycenter bonds, two-electron-three-center (2e3c) bonds and one-electron-two-center (1e2c) bonds of various types. Goal is to develop a generalized description of chemical bonds involving boron atoms across the different allotropes and compounds.