FIGURE 4 The highest occupied molecular orbitals (HOMOs) (isovalue = 0.02) of OLi3-doped GY/GDY/GTY
Table 1 also collects the interaction energies (E int) between OM3 and GYs. From Table 1, all systems exhibit remarkably largeE int values ranging from –34.97 to –61.15 kcal mol-1, indicating that these salts possess high stability. Previous studies have shown that the alkali metal cation-GY anion interaction strength is related to the size of the model GY systems.56 A similar situation occurs in our system. For example, the varying order ofE int is –47.18 (OLi3+@GY) < –53.00 (OLi3+@GDY) < –61.15 kcal mol-1(OLi3+@GTY), indicating that the pore size of the graphyne is an influencing factor on the stability for such systems. The more acetylene units are involved, the higher the stability of the complex salts. In particular, three OLi3-doped salts have the largestE int values among three types of graphynes, respectively, demonstrating that the interactions between the OLi3 units and the graphynes are much stronger. Hence, the OLi3+@GTY has the highest stability.
Additionally, the electronic stability of the complexes is associated with their vertical ionization potential (VIP). Table 1 shows that the VIP values of the OM3+@GYs salts are in the range of 4.25–4.83 eV, which are higher than those of electride Li@calix[4]pyrrole (4.16 eV) and superalkali-based alkalides M31 ·K (M = Li, Na, K;1 =all-cis -1,2,3,4,5,6-hexafluorocyclohexane) (3.088–3.275 eV).57,58The higher VIP values suggest that these superalkali salts of graphynes exhibit higher electronic stability. Besides, the VIPs of these OM3+@GYs salts are comparable to those of reported superalkali-doped M2X@GDY (M = Li, Na, K and X = F, Cl, Br) systems (4.59–5.20 eV).36 It could be observed that as the atomic number of alkali metals increases, the positive charge on OM3 in the OM3+@GYs system gradually increases, while the corresponding VIP value gradually decreases. For example, the M charge varies in the order 0.473 (M = Li) < 0.589 (M = Na) < 0.666 |e | (M = K), and the VIP order is 4.61 (M = Li) > 4.52 (M = Na) > 4.25 eV (M = K) for OM3+@GDY (Table 1).