Metal–Organic Frameworks for Highly Selective Separation of Xylene Isomers and Single-Crystal X-ray Study of Aromatic Guest–Host Inclusion Compounds

Separation of hydrocarbon molecules, such as benzene/cyclohexane and o -xylene/ m -xylene/ p -xylene, is relevant due to their widespread application as chemical feedstock but challenging because of their similar boiling points and close molecular sizes. Physisorption separation could offer an energy-efficient solution to this problem, but the design and synthesis of sorbents that exhibit high selectivity for one of the hydrocarbons remain a largely unmet challenge. Herein, we report a new heterometallic MOF with a unique tortuous shape of channels decorated with aromatic sorption sites [Li 2 Zn 2 (bpy)(ndc) 3 ] ( NIIC-30(Ph) , bpy = 4,4'-bipyridine, ndc 2- = naphthalene-1,4-dicarboxylate) and study of its benzene/cyclohexane and xylene vapor and liquid separation. For an equimolar benzene/cyclohexane mixture, it is possible to achieve a 10-fold excess of benzene in the adsorbed phase. In the case of xylenes, microporous framework NIIC-30(Ph) demonstrates outstanding selective sorption properties and becomes a new benchmark for m -/ o -xylene separation. In addition, NIIC-30(Ph) is stable enough to carry out at least three separation cycles of benzene/cyclohexane mixtures or ternary o -xylene/ m -xylene/ p -xylene mixtures both in the liquid and in the vapor phase. Insights into the performance of NIIC-30(Ph) are gained from X-ray structural studies of each aromatic guest inclusion compound.