The π-Tetrel Bond and its Influence on Hydrogen Bonding and Proton Transfer

The positive region that lies above the plane of F2TO (T=C and Si) interacts with malondialdehyde (MDA), which contains an intramolecular H-bond. The T atom of F2TO can lie either in the MDA molecular plane, forming a TO tetrel bond, or F2TO can stack directly above MDA in a parallel arrangement. The former structure is more stable than the latter, and in either case, F2SiO engages in a much stronger interaction than does F2CO, reaching nearly 200kJmol(-1). The -tetrel bond strengthens/weakens the MDA H-bond when the bond is formed to the hydroxyl/carbonyl group of MDA, and causes an accompanying inhibition/promotion of proton transfer within this H-bond; this effect is stronger for F2SiO. These same aspects can be tuned by substituents placed on any of the C atoms of MDA, although their effects are not fully correlated with the electron-withdrawing or electron-releasing properties of the substituent. A new type of - tetrel bond occurs when the -hole on the T atom of F2TO approaches the middle carbon atom of MDA from above, and a similar configuration is also found between F2TO and benzene. Evidence for extensive CC - tetrel bonding in crystal materials is presented.