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.