An adsorbate biased dynamic 3D porous framework for inverse CO sieving over CH.

Separating carbon dioxide (CO) from acetylene (CH) 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(μ-OH)(μ-OH)(1,4-ndc)} (1,4-ndc = 1,4-naphthalenedicarboxylate) with a one-dimensional pore channel (3.05 × 3.57 Å), that perfectly matches with the molecular size of CO and CH. 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 adsorption at 195, 273, and 298 K, but not for CH. The real time breakthrough gas separation experiments reveal a rarely attempted inverse CO selectivity over CH, attributed to open metal sites with a perfect pore aperture. This is supported by crystallographic analysis, spectroscopic inspection, and selectivity approximations. DRIFTS measurements and DFT-based theoretical calculations confirm CO binding sites are coordinatively unsaturated Ni(ii) and carboxylate oxygen atoms, and highlight the influence of multiple adsorption sites.