团簇As_4S与As_4Se稳定性与芳香性的理论研究

Theoretical Study on Stability and Aromaticity of As_4S and As_4Se Clusters

结合密度泛函和二级微扰理论,对As4S和As4Se团簇进行结构优化和频率分析.结果表明两者基态都采取单重态平面五角形构型(C2v,1A1)。分子轨道分析表明每个基态都有三个双电子占据的、高度离域的π型价分子轨道,符合4N+2芳香性电子规则。所有相邻As–As、As–M(M=S,Se)键的Wiberg键级(自然键轨道分析)和键长都处于相应单、双键数值之间;预测的各向异性磁化率和核独立化学位移都为较大负值,以上证据充分表明As4S和As4Se基态都表现出强芳香性。

Structural optimizations and harmonic vibrational frequency analyses on doped As4M（M=S,Se） clusters were carried out combining DFT and MP2 theory levels.Results showed both their ground states adopt singlet planar pentagonal structures（C2v,1A1）.Molecular orbital analyses reveal each ground state has three doubly occupied,delocalized valance π MOs,thus fulfilling 4N＋2 electron counting rule.The Wiberg bond index（NBO analyses） and optimized bond lengths of all adjacent As–As,As–M（M=S,Se） bonds are intermediate of corresponding values for singlet-,doublet-bonds.The big negative magnetic susceptibility anisotropies and nucleus-independent chemical shifts along with the above evidences confirmed that As4S,As4Se ground states exhibit strong aromatic characters.