Phyical Chemistry Chemical Physics
Royal Society of Chemistry
One of several tetrel (T) atoms was covalently attached to three F atoms and a substituted phenyl ring. A NH3 base can form a tetrel bond with TF3C6H2R3(T = Si, Ge, Sn, Pb; R = H, F, CH3) in a position opposite either an F atom or the ring. The σ-hole opposite the highly electron-withdrawing F (T-F) is more intense than that opposite the ring (T-C). However, when the Lewis base deforms from a tetrahedral to a trigonal bipyramidal shape so as to accommodate the base, it is the T-C σ-hole that is more intense. Accordingly, it is the T-C tetrel-bonded complex for which there is a larger interaction energy with NH3, as high as 34 kcal/mol. Countering this trend, it requires more energy for the TF3C6H2R3 to deform into the geometry it adopts within the T-C complex than within its T-F counterpart. There is consequently a balance between the overall binding energies of the two competing sites. The smaller tetrel atoms Si and Ge, with their larger deformation energies, show a preference for T-F tetrel binding, while the T-C site is preferred by Pb which suffers from a smaller degree of deformation energy. There is a near balance for T=Sn and the two sites show comparable binding energies.
Wysokiński, R., Michalczyk, M., Zierkiewicz, W., Scheiner, S. I. (2019). Influence of monomer deformation on the competition between two types of σ-holes in tetrel bonds. Phys. Chem. Chem. Phys., 21(20), 10336-10346. http://dx.doi.org/10.1039/C9CP01759C