4 | CONCLUSION
In this study, ab initio and QTAIM studies were performed to explore the nature of halogen bonds and some other noncovalent bonds in a series of crystal structure geometries of 1,2-diiodoolefins. Theab initio calculations were carried out at the B3LYP-D3/6-311++G(d,p) and B3LYP-D3/def2-TZVP levels of theory for both crystal and optimized monomers and dimers. Firstly, the calculation results show deviations between the two levels of theory to be quite small. Secondly, the computational values for optimized structures are close to the values for crystal structures.
The reported results provide important information concerning the physical chemistry of these materials. In particular, the crystal geometrical architecture and intermolecular bonding properties were shown to be reproducible with the calculations. The interaction energy and electron density appear to be appropriate tools to judge the stabilities of the crystal structures. Quantification of the noncovalent bonding energy between the molecules in dimers was evaluated both on the crystal and optimized structures, and the interaction energies were within 11.67 kJ·mol-1 and 44.55 kJ·mol-1 with B3LYP-D3/6-311++G(d,p). The intermolecular interactions responsible for the formation of the dimers are weak-to-moderate in strength, these interactions were clearly of enough local significance to guide the solid state crystallization process. Moreover, for the halogen bonds of type I…I, I…O and I…C(π), there is a strong linear relationship between the electron densities ρ (b) and the bond lengths. This confirms the relationships between electron density and the stability of halogen bonds.