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
M3O·1 ·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).