Guin Surajit, Ghosh Sourav Ranjan, Jana Atish Dipankar
Department of Physics, Behala College, Parnasree, Kolkata, 700060, India.
Department of Physics, Behala College, Parnasree, Kolkata, 700060, India; Department of Physics, Heritage Institute of Technology, Kolkata, 700107, India.
J Mol Graph Model. 2020 Jun;97:107544. doi: 10.1016/j.jmgm.2020.107544. Epub 2020 Jan 23.
A pair of Al 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.
最近我们小组报道了一对铝簇，一个是完美平面结构（CI），另一个是准平面结构（CII）[Guin等人，《分子模拟杂志》，2018年，24卷，344页]。这两个簇都是具有独特芳香特性的金属芳香体系的罕见例子。在这些簇中，局部强反芳香δ嵌入在强芳香海中。准平面CII结构是具有零虚频的真正最小结构，但平面CI结构被发现有三个虚频。进一步寻找具有单个虚频的可能过渡结构（CT）取得了成功，这表明CT结构也是准平面的，但与尾部向上褶皱的CII簇相比，该簇的尾部区域向下褶皱。对这三个簇进行了比较电子结构分析，这为三种状态之间的转变方式提供了见解。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，CI似乎具有介于向下褶皱的CT和向上褶皱的CII之间的中间几何结构。对所有三个簇的NICS、ELF、AIM和LOL比较分析表明，全局芳香性质按CT、CI、CII的顺序增加。一项TDDFT研究表明，CT和CII簇的振子强度彼此非常接近，比平面CI簇高一个数量级。
