阳离子X_3^+(X=Sc,Y,La)团簇d轨道芳香性的理论研究  

Theoretical study on the aromaticity from d-AOs in cationic X_3^+(X=Sc,Y,La) clusters

作　　者：池贤兴[1] 林行展[1] 

机构地区：[1]温州大学物理与电子信息工程学院,温州325035

出　　处：《原子与分子物理学报》2010年第4期663-672,共10页Journal of Atomic and Molecular Physics

基　　金：浙江省自然科学基金(102069)

摘　　要：运用密度泛函(DFT)和关联从头算(correlated ab initio)理论,对阳离子X_3^+(X=Sc、Y、La)和相关的中性X_3Cl(X=Sc、Y、La)团簇的稳定结构与芳香性进行研究.计算结果表明,X_3^+阳离子有两个稳定异构体:正三角型(D_(3h))和线型(D_(∞h)),其中正三角型为基态.对于中性的X_3Cl团簇,Sc_3Cl有三个稳定的异构体:三角金字塔型(C_(3v))、双齿型(C_(2v)-1)和C_(2v)-2型(图1);而Y_3Cl和La_3Cl只有2个稳定的异构体:三角金字塔型(C_(3v))和双齿型(C_(2v)-1).但这三个中性X_3Cl团簇的基态都是双齿型(C_(2v)-1)结构.对阳离子正三角型(D_(3h))基态结构进行共振能(RE)和核独立化学位移(NICS)的计算结果表明,X_3^+正三角型异构体展现出较高的芳香性.详细的分子轨道分析显示,正三角型Sc_3^+和Y_3^+阳离子有一个离域的π型分子轨道,显现出单π-芳香性;而正三角型La_3^+阳离子有一个离域的σ型分子轨道,显现出单σ-芳香性.X_3^+单π-芳香性或单σ-芳香性主要源于过渡金属Sc、Y和La的d原子轨道的贡献.另外,通过分子轨道分析还发现,当一个补偿阴离子Cl^-分别与Sc_3^+、Y_3^+阳离子结合成中性Sc_3Cl、Y_3Cl团簇时,其组成单元Sc_3^+、Y_3^+的芳香类型从原π-芳香性变为σ-芳香性,而当一个补偿阴离子Cl^-与La_3^+阳离子结合成中性La_3Cl时,其组成单元La_3^+原σ-芳香性保持不变.换言之,三个中性X_3Cl团簇都只显现出单σ-芳香性.The stable structures and aromatic characters for three cationic X＋ （X=Sc, Y, and La） and three relevant neutral X3 Cl （X= Sc, Y, La） clusters are investigated with density functional and correlated ab initio theory. The calculated results show that the X3^＋ cations each has two stable structures, the regular trigon （D3h） and the linear （D∞h） with the regular trigon （D3h） being the ground state, while for three neutral X3 Clclusters, Sc3 CI has three stable isomers, the trigon-pyramidal （Cv）, bidentate （C2v- 1）, and C2v-2 structures, Y3Cl and La3Cl each has only two stable isomers： the trigon-pyramidal （C3v） and bidentate （C2v-1） structures. The ground states for three X3Cl species are all the bidentate （C2v- 1） isomers. The calculations of the resonance energy （RE） and NICS show that trigonal X3^＋ isomers exhibit higher degree of aromaticity. The detailed molecular orbital （MO） analyses reveal that the isolated trigonal Sc3^＋ and Y3^＋ cations each has one delocalized π-type MO and shows single π-aromaticity, while the isolated trigonal La3^＋ cation has one delocalized σ-type MO and shows single a-aromatieity. The single π- or σ-aromaticity for X3^＋ are attributed to the contributions mainly from the d AOs of the corresponding transition metal X atoms. But, when a singly negatively charged counterion Cl^- is added to Sc3^＋ , Y3^＋, and La3^＋ cations respectively, the aromatic type for the two Sc＋, Y＋ units in the corresponding neutral Sc3 Cl, Y3 Cl complexes are changed from π-aromaticity into σ- aromaticity, whereas the σ-aromaticity of the La3^＋ units in the La3Cl complex keeps unchanged in this process. Thus three Sc3^＋ , Y3^＋, La3^＋ units in the corresponding X3Cl complexes all have only one a-type MO and exhibit single a-aromaticity.

关 键 词：过度金属团簇 密度泛函理论 芳香性 分子轨道分析 

分 类 号：O641[理学—物理化学]