Theoretical study of aromaticity in small hydrogen and metal cation clusters X +3 (X=H, Li, Na, K, and Cu)

• Published in: International journal of quantum chemistry 2007, Vol.107 (3), p.722-728
• Main Authors: Yong, Liu, Wu, Shao Dan, Chi, Xian Xing
• Format: Article
• Language: English
• Subjects: ab initio; aromaticity; metal clusters; NICS; resonance energy
• ISSN: 0020-7608; 1097-461X
• DOI: 10.1002/qua.21166

Five cation clusters X +3 (X=H, Li, Na, K, and Cu) with two possible isomers, i.e., regular trigonal structure (D3h) and linear structure (D∞h), have been investigated using four methods: B3LYP, B3PW91, MP2, CCSD(T) and basis set 6‐311+G(3df). The calculations show that only the regular trigonal structure (D3h) is stable. The related neutral clusters X3Cl (X=H, Li, Na, K, and Cu) are also investigated using two methods: B3LYP, MP2, and basis set 6‐311+G(3df). For H3Cl species, there is no a stable structure to be found. For other four X3Cl (X=Li, Na, K, and Cu) species, there are two stable isomers, for which the bidentate structures (C2v‐1) [see Fig. 1(d)] are global minima. According to the general criteria for aromaticity including resonance energy (RE) and nucleus‐independent chemical shift (NICS), the five trigonal isomers exhibit a higher degree of aromaticity. Molecular orbital analysis reveals that the five trigonal X +3(X=H, Li, Na, K, and Cu) isomers possess only σ‐aromaticity originating from s orbitals. For the Cu +3 ring the d orbitals do not play a significant role in the electron delocalization effects. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007