On the nature of bonding in binary Be2O2 and Si2O2 clusters: rhombic four-center four-electron π and σ bonds. Issue 14 (21st March 2016)

• Record Type: Journal Article
• Authors: Wang, Kang; Wang, Ying-Jin; Li, Da-Zhi; Ou, Ting; Zhao, Xiao-Yun; Zhai, Hua-Jin
• Is Part Of: Physical chemistry chemical physics. Volume 18:Issue 14(2016)
• Page Start: 9594
• Page End: 9601
• Publication Date: 2016-03-21
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c6cp00532b
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Multifold (π and σ) four-center four-electron o-bonds are uncovered in rhombic Be2 O2 and Si2 O2 binary clusters, which are considered to be aromatic. Abstract : The structural and electronic properties and chemical bonding of binary Be2 O2 and Si2 O2 clusters have been studied using quantum chemical calculations at the B3LYP level. For the Be2 O2 cluster, the potential energy surface is probed by unbiased structural searches and the global-minimum structure was established using the B3LYP calculations, complemented by PBE0 and single-point CCSD(T) calculations for top isomers. The perfectly planar D 2h Be2 O2 ( 1 Ag ) global minimum is well defined, being at least 3.64 eV lower in energy than alternative structures at the CCSD(T)//B3LYP/aug-cc-pVTZ level. Chemical bonding analyses show that D 2h Be2 O2 and Si2 O2 clusters possess the rhombic four-center four-electron (4c–4e) π bond, that is, the o-bond, a conception derived from electron-deficient boron oxide clusters lately. Furthermore, the Be2 O2 and Si2 O2 clusters also exhibit rhombic 4c–4e σ bonds, both for the radial and tangential σ frameworks (σr and σt ). The σt framework is classified as an o-bond only formally, due to the secondary contribution from the Be/Si s component. The three-fold (π, σr, and σt ) o-bonds in Be2 O2 and Si2 O2 are considered to resemble the three-fold aromaticity in all-metal Al4 2− dianions. A 4c–4e o-bond makes use of four O 2p electrons, which would otherwise be two lone-pairs, for a delocalized and completely bonding orbital, as well as a residual nonbonding orbital. Three-fold o-bonds thus greatly stabilize the binary Be2 O2 and Si2 O2 clusters. We anticipate that the bonding concept should be applicable to additional molecular systems, including those with larger heterocyclic rings.