Separation of toluene from benzene derivatives and extraction of toluene from water based on a flexible naphthalene diimide coordination network

The separation of toluene derivatives from each other is an important, challenging, and energy exhaustive process in chemical industry. Here we report a new flexible coordination network, [Cu(4-pmntd)₂(NO₃)₂](4-pmntd = N, N’-Bis(4-pyridymethy)naphthalene diimide), that exhibits not only selective separation of toluene over benzene and xylene, but also can straight extract toluene from water. The high performance for selective adsorption of toluene was validated by single-crystal XRD, vapor sorption isotherms, and NMR. The detailed structural information discloses that the naphthalene diimide derivative ligand can form intermolecular charge-transfer interactions with toluene, and thus highly selective capture toluene with its derivatives. Naphthalene diimide ligand engenders favorable aromatic π interactions for its electron-deficient and planar aromatic surface. The electron giving substituents on aromatic ring cause an overall change in the cloud density, which can be employed in separating toluene derivatives. When 1:1 toluene/benzene mixture pass through a fixed-bed packed column with this coordination network, 96% purity of benzene can be directly produced during the first adsorption cycle. The outlet xylene purity was raised from 50% to 85% when 1:1 toluene/xylene mixture pass through the porous materials. The separation performance of the coordination network could be used for industrial separation of toluene derivatives with a low energy cost at room temperature.