Record-Setting Selectivity for -Xylene by an Intrinsically Porous Zero-Dimensional Metallocycle.

In its crystalline state, a dinuclear Cu-based metallocycle discriminates between the three isomers of xylene with liquid-phase selectivity in the order -xylene ≫ -xylene ≫ -xylene. This selectivity holds over a wide concentration range, with -xylene concentrations as low as 5%. Single-crystal X-ray diffraction and gas chromatography further indicate that the metallocyclic host extracts trace amounts of -xylene from commercially pure -xylene (≥99%); using NMR spectroscopy, we show that the metallocycle exhibits exclusive selectivity for -xylene. Crystallographic studies show that the selectivity is based on the size and shape of the guest in combination with the flexibility of the host.