Adsorption of formaldehyde on the flexible building block of FCOF-5

Recently, flexible C-O single bonds in the building block backbone was introduced to flexible covalent organic frameworks-5 (FCOF-5) that the breathing behavior upon vapor adsorption and desorption was revealed. In this work, the adsorption of formaldehyde on the flexible building block of FCOF-5 was theoretically investigated using density function theory (DFT) and second-order Møller-Plesset perturbation theory (MP2) in conjunction with the 6-31G(d) and 6-311G(d,p) basis sets. The calculated results showed that benzyloxybenzene (BO1) was the most stable conformation, resulting in the shortest H-bond distance of 2.46 Å. The strongest interaction energy of BO1 with basis set superposition errors (BSSE) correction is -12.04 kJ/mol obtained from the MP2/6-311G(d,p) level of theory, demonstrating most preference adsorption site of formaldehyde. The existence of the C-H…π interaction in formaldehyde…benzyloxybenzene (BO6-BO9) complexes was also found with interaction energies ranging from -7.47 to -9.38 kJ/mol. A high rotational C-O bond was demonstrated upon exposure to formaldehyde corresponding to a significant change in torsion angles (123^o -147^o).