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.