Bridging a Knowledge Gap from Siloxanes to Germoxanes and Stannoxanes. A Theoretical Natural Bond Orbital Study

Explaining the nature of the E-O chemical bond (E = Si, Ge, Sn) has been a great challenge for theoretical chemists during the last decades. Among the large number of models used for this purpose, the one based on hyperconjugative interactions sheds more light on the nature of chemical bonding in siloxanes. Starting from this concept, this study aimed to evaluate the impact of siloxane type hyperconjugative effects on the structural features of germoxanic and stannoxanic species and in addition to assess if p-d-like back-bonding interactions can also play important roles in determining the particular structures of these heavier analogues of ethers. Natural bond orbital deletion (NBO DEL) optimizations, carried out at the DFT level of theory, revealed that hyperconjugative effects dictate to a large extent the structural behavior of these species. Furthermore, this study points out that p-d back-bonding interactions also influence the equilibrium geometry of these species, although acting as a secondary electronic effect within the E-O-E moieties (E = Si, Ge, Sn).