Structural diversity, gas adsorption and magnetic properties of three coordination polymers based on a rigid multicarboxylate ligand

Abstract

Three Co(II) coordination polymers (CPs), {[Co₂(HL)(1,4-bibb)(H₂O)]·(CH₃CN)·(H₂O)}_n (1), {[Co₄(L)(OH)₃(H₂O)₄]·(1,4-bmib)}_n (2) and {[Co₆(L)₂(OH)₂(4,4-biyb)]·(CH₃CN)·(H₂O)}_n (3) have been obtained based on a V-shaped rigid pentacarboxylate ligand (H₅L = 3,5-di(2′,5′-dicarboxylphenyl)benzoic acid) and different N-donor ligands. All complexes show 3D structures and contain open carboxyl sites and “accessible metal sites” (AMSs). The gas adsorption experiments show that 1 and 3 have a high H₂ adsorption capacity at 77 K and in particular, 3 displays the selective uptake of CO₂ over CH₄ (14.2 for CO₂/CH₄ = 0.5/0.5 and 11.0 for CO₂/CH₄ = 0.05/0.95 under 1 bar at 298 K). Furthermore, anti-ferromagnetic interactions among Co(II) ions are observed in 2.