The role of C–H⋯π interactions in modulating the breathing amplitude of a 2D square lattice net: alcohol sorption studies

Abstract

A breathing 2D net 1 {[Zn(34pba)₂]·DMF}_n assembled from mononuclear zinc(II) centres and 3-(4-pyridyl) benzoate (34pba) ditopic linker is presented. 1 undergoes a displacive phase transition to give 1d, [Zn(34pba)₂]_n on evacuation of DMF. This is accompanied by a 37% decrease in solvent accessible void volume. Exposure of 1d to alcohol vapours shows that the saturation uptake increases with an increase in number of carbon atoms in the alcohol. The enhanced uptake of n-butanol and n-propanol is attributed to the long alkyl chain which enhances C–H⋯π interactions with the hydrophobic pyridyl and phenyl rings of the network. These interactions trigger the breathing motion of the 2D network and allow for the entry of n-propanol and n-butanol into the channels. Methanol and ethanol are unable to initiate the dynamic motion of the framework which increases the channel volume. In consequence, these solvents are absorbed to a lesser extent. Vapour phase competition studies show that the activated material is able to absorb n-butanol in the presence of a high vapour pressure of methanol. The selectivity observed may be based on factors that allow the metal organic framework inclusion compound to assume the most relaxed conformation.