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.)