Strain in nonclassical silicon hydrides: An insight into the "ultrastability" of sila-bi[6]prismane (Si18H12) cluster with the endohedrally trapped silicon atom, Si19H12

• Published in: Journal of computational chemistry 2015-10, Vol.36 (28), p.2095-2102
• Main Authors: Dolgonos, Grygoriy A., Mekalka, Koshka
• Format: Article
• Language: English
• Subjects: ab initio calculations; prismanes; silicon hydrides; silicon nanoclusters; strain energy
• ISSN: 0192-8651; 1096-987X
• DOI: 10.1002/jcc.24014

The recently postulated concept of “ultrastability” and “electron‐deficient aromaticity” (Vach, Nano Lett 2011, 11, 5477; Vach, J Chem Theory Comput 2012, 8, 2088) in a sila‐bi[6]prismane having an additional entrapped silicon atom, Si19H12, has been disproved on the basis of a careful analysis of the energetic characteristics related to the formation of this and other silicon hydrides. The central silicon atom in Si19H12 is weaker bound to other silicon atoms than in conventional tetrahedral silanes; moreover, Si19H12 possesses a significant amount of strain. The role of strain in the formation of the title compounds has been further rationalized by calculating the relative energies for the transformation to a half‐planar conformation in methane and in silane and by calculating the respective strain energies. The strain energy value in Si18H12 is equal to 9.93 eV whereas the same property for Si19H12 lies in range of 6.42–8.85 eV. Two low‐energy isomers of Si19H12 which lie by 2.77 and 3.42 eV (!) lower in energy than the originally considered sila‐bi[6]prismane‐based structure have been proposed. © 2015 Wiley Periodicals, Inc. The formation of a tubular silicon hydride nanocluster bearing nontetrahedral atomic configurations requires a significant amount of energy. As in the case of recently proposed tubular “ultrastable” sila‐bi[6]prismane with one encaged silicon atom, Si19H12, the energy difference with respect to the tetrahedral reference molecules (called “strain energy”) is high enough to cause isomerization or fragmentation reactions. Consequently, this isomer cannot be considered as “ultrastable” nor as aromatic. Two new low‐lying Si19H12 isomers have been proposed.