Enhanced CO₂ sorption properties in a polarizable [WO₂F₄]^2--pillared physisorbent under direct air capture conditions

We report the CO₂ capture properties of an ultramicroporous physisorbent [Ni(WO₂F₄)(pyrazine)₂], WO₂F₄-1-Ni, which crystallizes in I4/mcm (a = 9.91785(6) Å, c = 15.71516(9) Å) and its structure is solved using laboratory X-ray powder diffraction. The WO₂F₄ 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 CO₂ capture properties has not been studied. In this context, at a 400 ppm partial pressure of CO₂ (applicable for direct air capture), this primitive cubic (pcu) network captures 0.934 mmol_CO g_sorbent^-1 under dry conditions and 0.685 mmol_CO g_sorbent^-1 at 75%RH, the highest capacity for a physisorbent reported to date.