Enhanced CO 2 sorption properties in a polarizable [WO 2 F 4 ] 2- -pillared physisorbent under direct air capture conditions.

We report the CO 2 capture properties of an ultramicroporous physisorbent [Ni(WO 2 F 4 )(pyrazine) 2 ] n , WO 2 F 4 -1-Ni, which crystallizes in I 4/ mcm ( a = 9.91785(6) Å, c = 15.71516(9) Å) and its structure is solved using laboratory X-ray powder diffraction. The WO 2 F 4 anion is acentric with polarizable WO bonds offering unique potential properties within a porous structure. Despite isostructural compounds being previously reported, the effect of this distorted anion on CO 2 capture properties has not been studied. In this context, at a 400 ppm partial pressure of CO 2 (applicable for direct air capture), this primitive cubic (pcu) network captures 0.934 mmol CO 2 g sorbent -1 under dry conditions and 0.685 mmol CO 2 g sorbent -1 at 75%RH, the highest capacity for a physisorbent reported to date.