摘要
An octahedral Nb6 structural unit with space aromaticity is identified for the first time in a transition–metal monoxide crystal Nb3O3 by ab initio calculations.The strong Nb–Nb metallic bonding facilitates the formation of stable octahedral Nb6 structural units and the release of delocalization energy.Moreover,the Nb atoms in continuously connected Nb6 structural units share their electrons with each other in a continuous space of framework,so that the electrons are uniformly distributed.The newly discovered aromaticity in the octahedral Nb6 structural units extends the range of aromatic compounds and broadens our vision in structural chemistry.
通过对NbO氧化物的研究,本文发现NbO的周期性晶体结构中存在Nb6立体芳香性结构基元.每个Nb原子周围有4个O原子在平面配位,形成相对罕见的平面四配位结构基元.氧的空缺打破了通常的NbO6八面体对称性,因而其轨道能级也发生分裂重排.原本八面体高对称性下简并的eg和t2g轨道发生了分裂,eg中分裂出的dz2能级与t2g中分裂出dxz,dyz能量靠近和交错,增加了不同Nb原子间d轨道能级在能量上的匹配.在Nb3O3晶体中,由于Nb原子间的d轨道的能量和空间对称性的互相匹配,d轨道可以互相叠加成强烈的金属键,这些金属键有助于形成芳香性的Nb6八面体原子簇.这些八面体再共用顶点的Nb连接成三维骨架,而使得NbO具有金属Nb那样的金属光泽和导电性.
基金
financially supported by National Key R&D Program of China(2016YFB0700600)
Soft Science Research Project of Guangdong Province(2017B030301013)
Shenzhen Science and Technology Research Grant(ZDSYS201707281026184).
