FIGURE 3 Optimized structures of OM3@(GY/GDY/GTY) (M = Li, Na, and K)
unit of OM3@GY (M = Li, Na, and K) exhibits a slight corrugation, especially for ONa3@GY. In contrast, the OM3 units in OM3@GDY (M = Li, Na, and K) are all above the central position of the pore and the three alkali atoms point to three benzene rings, respectively. It is clearly seen that the structural features of (ONa3/OK3)@GTY are similar to those of OM3@GDY. Interestingly, unlike other structures, small-sized OLi3 is embedded inside the large pore of GTY, which leads to a planar structure of OLi3@GDY, as shown in red box in Figure 3. Except for OLi3 in OLi3@GTY, all the other OM3 units distort from a triangle to an umbrella shape. Table 1 shows that average O–M bonds of the OM3 unit in OM3@(GY/GDY/GTY) are slightly elongated compared with the corresponding O–Li (1.683), O–Na (2.053), and O–K (2.404 Å) bonds in isolated OM3. This indicates that the interaction between OM3 and GYs has little impact on the M–O chemical bonds. The vertical distance (d ) between OM3 and the graphyne surface (GY, GDY, and GTY) is also given in the table, which exhibits an increasing trend with increasing atomic number of M.
TABLE 1 The average O–M bond lengthsR O–M (Å), vertical distances between the O atom and plane d (Å), interaction energies E int(kcal mol-1), MK charges on the OM3units q (|e |), and vertical ionization potentials VIP (eV) of the OM3@GYs (M = Li, Na, and K)