An adsorbate biased dynamic 3D porous framework for inverse CO 2 sieving over C 2 H 2 .

Separating carbon dioxide (CO 2 ) from acetylene (C 2 H 2 ) is one of the most critical and complex industrial separations due to similarities in physicochemical properties and molecular dimensions. Herein, we report a novel Ni-based three-dimensional framework {[Ni 4 (μ 3 -OH) 2 (μ 2 -OH 2 ) 2 (1,4-ndc) 3 ](3H 2 O)} n (1,4-ndc = 1,4-naphthalenedicarboxylate) with a one-dimensional pore channel (3.05 × 3.57 Å 2 ), that perfectly matches with the molecular size of CO 2 and C 2 H 2 . The dehydrated framework shows structural transformation, decorated with an unsaturated Ni(ii) centre and pendant oxygen atoms. The dynamic nature of the framework is evident by displaying a multistep gate opening type CO 2 adsorption at 195, 273, and 298 K, but not for C 2 H 2 . The real time breakthrough gas separation experiments reveal a rarely attempted inverse CO 2 selectivity over C 2 H 2 , attributed to open metal sites with a perfect pore aperture. This is supported by crystallographic analysis, in situ spectroscopic inspection, and selectivity approximations. In situ DRIFTS measurements and DFT-based theoretical calculations confirm CO 2 binding sites are coordinatively unsaturated Ni(ii) and carboxylate oxygen atoms, and highlight the influence of multiple adsorption sites.