Figure 11 . The linear relationship between the cooperative energy E coop versus the changes of the changes of Vmin (ΔVmin) on the free N atom in X…CN-Ph-CN and Y…Br-Ph-CN dimers compared with the corresponding R-Ph-CN monomers.

3.2.4 AIM and NBO analyses

Table 7 presents the topological parameters in some representative dimers and trimers. The positive Laplacian ∇2ρBCP and the negative HBCP at the N…P and B…N BCPs indicate that both the pnicogen bonding and triel bonding belong to partially covalent interactions. The synergistic effect is also manifested in the changes of the electron density at the BCPs in the trimer in comparison with the dimers, since the ρBCP can be used to estimate the strength of the intermolecular interactions. The ρBCP at Hal…P (Hal=F, Cl, Br) and N…P BCPs decreases in X…CN-Ph-CN…PO2F complexes, while that at Br…N and N…P BCPs increases in the Y…Br-Ph-CN…PO2F complexes. These changes of ρBCP are consistent with theE coop we obtained. Different variations occur for the BH3…CN-Ph-CN…PO2F and BF3…CN-Ph-CN…PO2F complexes. For the former, the ρBCP at B…N BCP increases from 0.0880 to 0.1186 a.u. in comparison with that in BH3…CN-Ph-CN dimer, while for the latter, it decreases from 0.0884 a.u. in dimer to 0.0216 a.u. in trimer. These B…N bonding changes are consistent with the variations of the B…N distance, which decreases from 1.543 to 1.537 Å for the former, and increase from 1.824 to 2.405 Å for the latter, respectively.
Table 7. The AIM topological analysis of some representative binary and ternary complexes (Unit: a.u.)