Weak interactions between trivalent pnictogen centers: computational analysis of bonding in dimers X3E...EX3 (E = pnictogen, X = halogen).

The nature of weak interactions in dimers X(3)E...EX(3) (E = N-Bi, X = F-I) was investigated by wave function and density functional theory (DFT)-based methods. Out of the 20 systems studied, 10 are found to be bound at the CP-MP2 and LMP2 levels of theory. Detailed partition of the interaction energy into different components revealed that dispersion is the primary force holding the dimers together but there also exists an important ionic component whose contribution increases with increasing halogen size. As expected, standard density functionals fail to describe bonding in the studied systems. However, the performance of DFT methods can be easily improved via empirical dispersion correction though full agreement with high level ab initio results was not obtained. Total binding energies calculated at the SCS-MP2 and LCCSD(T) levels of theory yield an energy scale of 10-15 kJ mol(-1) which is comparable to a weak hydrogen bond and demonstrates that E...E interactions, and P...P interactions in particular, can be considered relevant for determining supramolecular structure in the solid state. In addition to high-level energy estimates, results from detailed bonding analysis showed that group 13 dimetallenes are structural analogues of the studied dimers, and as such contain a slipped pi-interaction which is antibonding in nature.