A tetrel bond (TtB) is an attractive interaction between an electrophilic element of group 14 and a nucleophile. Experimental data and theoretical calculations show that if, in an intramolecular tetrel-bonded system, the electrophilic tetrel atom Tt is connected to the nucleophilic atom through alternating single and double bonds within a supramolecular ring, the resonance resulting from π-electron conjugation/delocalization strengthens the TtB. These TtBs with conjugation/delocalization tend to be shorter and closer to linearity than analogous TtBs in rings wherein conjugation/delocalization is not possible. The TtBs, wherein π-electron conjugation/delocalization is present, are called resonance-assisted tetrel bonds (RATtBs) in analogy to the well-known resonance-assisted hydrogen bond (RAHB) proposed by the Gilli group. This work discusses several crystal structures from the Cambridge Structural Database (CSD) wherein the five tetrel atoms form RATtBs. Experimental data and theoretical calculations (QTAIM and NBO) prove that the strength and directionality of RATtBs can be regulated by varying the involved tetrel atom, the nucleophile, and the substituents bonded to or close to the interacting atoms. Importantly, calculations reveal that the interaction weakens significantly when the conjugation-delocalization along the covalent bridge connecting the electrophilic tetrel and the nucleophile is interrupted.
Almehmadi et al. (Thu,) studied this question.