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

尽管经过多年的深入研究，涉及硼原子的化学键仍未被理解。例如，在环境条件下，硼的哪一种同素异形体是稳定形态尚不清楚。本项目旨在通过单晶x射线衍射实验表征硼的同素异形体，如β - b106和α -四方硼，以及富硼固体，如B13C2和B50C2。根据最大熵法（MEM）对多极子（MP）模型进行结构改进和数据分析，将产生反映价电子空间分布的详细电子密度图。根据Bader的分子中原子（AIM）理论，电子密度的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二电子-二中心（2e2c）键外，我们预计硼原子的电子亏缺性质将导致各种类型的多中心键、二电子-三中心（2e3c）键和一电子-二中心（1e2c）键。目的是对不同同素异形体和化合物中涉及硼原子的化学键进行广义描述。

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.