Van der Waals forces in the perfluorinated metal-organic framework zinc 1,2-bis(4-pyridyl)ethane tetrafluoroterephthalate

Traditional density functional theory (DFT) and dispersion-corrected DFT calculations are performed to investigate the metal-organic framework zinc 1,2-bis(4-pyridyl)ethane tetrafluoroterephthalate (Znbpetpa). Without dispersion correction, straightening of the zigzag C-O-Zn chain connecting the secondary building units across the diagonal of the unit cell is observed, accompanied by a large anisotropic expansion of the structure along one cell parameter. The results show that van der Waals dispersion forces and specifically Zn-C equatorial interactions and the resulting effects on the zigzag chain play an important role in maintaining key structural features which match with experimental observations. It is suggested that the pore volume of the framework could be controlled by substituting the Zn metal centre with another transition element of different polarizability, while maintaining functional linkers.