A pair of Al₁₃⁺ clusters, one perfectly planar (CI) and another quasi-planar structure (CII) have been reported recently by our group [Guin et al. Journal of Molecular Modeling, 2018, 24, 344]. Both these clusters are rare examples of metal-aromatic systems having unique aromatic character. In these clusters, localized strong anti-aromatic deltas are embedded within a strong aromatic sea. The quasi-planar CII structure is a true minimum structure with zero imaginary frequency, but the planar CI structure has been found to have three imaginary frequencies. Further search for a possible transition structure (CT) with single imaginary frequency was successful, which shows that CT structure is also quasi-planar but the tail region of this cluster is puckered downward as compared to that of the CII cluster for which tail region is puckered upward. A comparative electronic structural analysis of these three clusters have been carried out which has provided insight into the way the transformation among the three states take place. Harmonic frequency analysis of these clusters reveals that transition from CT to CII occurs through the planar cluster CI that appears to have an intermediate geometry between the downwardly puckered CT and the upwardly puckered CII. A comparative NICS, ELF, AIM and LOL analysis of all three clusters reveal that the global aromatic nature increases in the sequence CT, CI, CII. A TDDFT study reveals that the oscillator strength of both CT and CII cluster is quite close to each other, which are one order of magnitude higher than the planar CI cluster.

一对Al ₁₃ ⁺最近，我们的研究小组报道了一个簇，一个完美的平面（CI）和另一个准平面的结构（CII）[Guin等。分子建模学报，2018，24，344]。这两个簇都是具有独特芳族特征的金属-芳族体系的罕见实例。在这些集群中，局部强反芳香三角洲被嵌入强芳香海中。准平面CII结构是虚数频率为零的真正最小结构，但已发现平面CI结构具有三个虚数频率。进一步搜索了一个具有单个虚数频率的可能过渡结构（CT）的尝试是成功的，这表明CT结构也是准平面的，但是与CII簇的尾部区域相比，该簇的尾部区域向下折叠。向上起皱。已经对这三个簇进行了比较电子结构分析，从而提供了对这三个状态之间转换方式的见解。对这些簇的谐波频率分析表明，从CT到CII的转变是通过平面簇CI发生的，该簇在下折CT和上折CII之间似乎具有中间几何形状。对所有三个簇的比较性NICS，ELF，AIM和LOL分析显示，总体芳香性以序列CT，CI，CII的形式增加。TDDFT研究表明，CT和CII簇的振荡器强度非常接近，比平面CI簇高一个数量级。