TABLE 4 is near here
Of all the dimers shown in Figure 4, dimer 2 possesses the smallest number of intermolecular noncovalent bonds: two halogen bonds of I…I and I…H. Its interaction energies calculated at the B3LYP-D3/6-311++G(d,p) level of theory are -9.58 kJ·mol-1 and -11.67 kJ·mol-1respectively for crystal and optimized geometries; and the respective values are -11.7 kJ·mol-1 and -12.57 kJ·mol-1 at the B3LYP-D3/def2-TZVP level of theory. Dimer 3 contains three halogen bonds of I…I, I…C(π), I2…C27(π), and I17…C12(π). Dimer 3 has the second highest interaction energy (Table 4) due to the two strong I…C(π) noncovalent bonds. Similarly, the I…C(π) noncovalent bond was also found in dimers 5 and 6; I23…C11(π) in dimer 5 and I1…C33(π) in dimer 6. Moreover, the halogen bond of type I…O was found in dimers 5 (I2…O25) and 6 (I27…O3). The respective interaction energies computed at the two levels of theory are -29.44 kJ·mol-1 and -32.02 kJ·mol-1­­ for crystal dimer 5 and -34.19 kJ·mol-1­­ and -31.79 kJ·mol-1­­ for the geometry optimized dimer 5. Equally, the respective interaction energies computed at the two levels of theory are -24.59 kJ·mol-1 and -26.45 kJ·mol-1­­ for crystal dimer 6 and -29.86 kJ·mol-1­­ and -27.00 kJ·mol-1­­ for the optimized dimer. The interaction energy in dimer 7b is also very high because there are five halogen bonds in dimer 7b: one I…I, one I…C(π) and three I…H, the details are shown in Figure 4 and Table 4. The highest interaction energy occurs in dimer 8, and the corresponding interaction energies computed at the two levels of theory are -36.75 kJ·mol-1 and -39.09 kJ·mol-1, respectively, for crystal dimer 8, and are -44.55 kJ·mol-1­­ and -39.95 kJ·mol-1­­ for optimized dimer 8. This Dimer has three halogen bonds of I…O, I…C(π) and I…H and one O…O noncovalent bond. To summarize, in Table 4, both the interaction energies (E_Int) and the BSSE energies (E_BSSE) for crystal dimers calculated at the two levels of theory are very close to the values for the optimized dimers. Therefore, the properties of halogen bonds can be calculated directly using the crystal structures without geometry optimization.