DOI
10.1007/s10904-025-03970-7
Abstract
The symmetry breaking in octahedral silsesquioxane and its germanium analogues (Si8O12H8 and Ge8O12H8) has been investigated using the M06-2X/6-31++G(3df, 3pd) method and group theory. Both structures undergo symmetry breaking, characterized by pseudo-Jahn−Teller stabilization energies of 0.22 kcal/mol for Si-POSS and 9.82 kcal/mol for Ge-POSS. Under the influence of the pseudo-Jahn–Teller effect, the distortion vector involves the vibrational a2g mode with imaginary frequency. The distortion forces in Oh-POSS are predominantly localized on the oxygen atoms and driven by the coupling between the lowest unoccupied molecular orbital (a1g) and the highest occupied molecular orbital (a2g). The symmetry breaking is attributed to a pseudo-Jahn–Teller mechanism of type (a2g x a1g) = a2g. The symmetrical substitution of oxygen atoms by X (where X = C, N, P) results in viable Th-Si8X12H8 and Th-Ge8X12H8 structures. The observed pseudo-Jahn–Teller distortion and substitutional symmetry breaking caused by X indicates a consistent electronic relaxation mechanism, characterized by the formation of C=C, N=N and P=P bonds on the POSS cubic faces, which serves as hallmarks of stability. Additionally, we find that the volume of substituted Th-symmetrical POSS is sufficiently large to accommodate small ions.
Document Type
Article
Publication Date
8-18-2025
Publisher Statement
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
Recommended Citation
Muya, J.T., Ceulemans, A. & Parish, C. Instability of the Octahedral Symmetry in Si8O12H8and Ge8O12H8: A Consequence of the Pseudo-Jahn–Teller Effect. J Inorg Organomet Polym35, 8584–8597 (2025). https://doi.org/10.1007/s10904-025-03970-7
