Density functional theory (DFT) cal

Density functional theory (DFT) calculations with the Gaussian 09 program on the model compound of COF-DHTA (Fig. 7) were accomplished to provide a theoretical basis and gain more understanding of the coordination of N and O atoms of COF-DHTA with Al3+ ions [44]. The complex of the model compound with Fe3+ ion was optimized at the B3LYP level [45] of density functional theory, together with vibrational frequency calculations to obtain minima of energy. Furthermore, the 6-31G (d,p) basis set was used to describe the C, H, O, and N atoms [46].