Supramolecular Interactions Induce Dynamics in Metal-Organic Layers to Selectively Separate Acetylene from Carbon Dioxide.

We report the synthesis and structural characterization of a 2D metal-organic framework with AB-packing layers, [Co 2 (pybz) 2 (CH 3 COO) 2 ]·DMF ( Co2 , pybz= 4-(4-pyridyl)benzoate), containing a stable (4,4)-grid network fabricated by paddle-wheel nodes, ditopic pybz, and acetate ligands. After removal of the guest, the layer structure is retained but reorganized into an ABCD packing mode in the activated phase ( Co2a ). Consequently, the intralayer square windows (7.2 × 5.0 Å 2 ) close, while the interlayer separation is decreased slightly from 3.69 to 3.45 Å, leaving a narrow gap. Importantly, the dangling methyl group of the acetate with H-bonds to the adjacent layers and also the well-distributed π-π interactions between the aromatic rings of neighboring layers facilitate the structural stability. These weak supramolecular interactions further allow for favorable dynamic exfoliation of the layers, which promotes efficient adsorption of C 2 H 2 (41.6 cm 3 g -1 ) over CO 2 with an adsorption ratio of 6.3 (0.5 bar, 298 K). The effective separation performance of equimolar C 2 H 2 /CO 2 was verified by cycling breakthrough experiments and was even tolerable to moisture (R.H = 52%). DFT calculations, in situ PXRD, and PDF characterization reveal that the favorable retention of C 2 H 2 rather than that of CO 2 is due to its H-bond formation with the paddle-wheel oxygen atoms that triggers the increase in interlayer separation during C 2 H 2 adsorption.