A novel bismuth-based metal-organic framework for high volumetric methane and carbon dioxide adsorption

Solvothermal reaction of H₄L (L=biphenyl-3,3′,5,5′- tetracarboxylate) and Bi(NO₃)₃·(H ₂O)₅ in a mixture of DMF/MeCN/H₂O in the presence of piperazine and nitric acid at 100-°C for 10 h affords the solvated metal-organic polymer [Bi₂(L)_1.5(H ₂O)₂]·(DMF)_3.5·(H ₂O)₃ (NOTT-220-solv). A single crystal X-ray structure determination confirms that it crystallises in space group P2/c and has a neutral and non-interpenetrated structure comprising binuclear {Bi₂} centres bridged by tetracarboxylate ligands. NOTT-220-solv shows a 3,6-connected network having a framework topology with a {4·6²} ₂{4²·6⁵·8⁸}{6 ²·8} point symbol. The desolvated material NOTT-220a shows exceptionally high adsorption uptakes for CH₄ and CO₂ on a volumetric basis at moderate pressures and temperatures with a CO₂ uptake of 553 g-L^-1 (20 bar, 293 K) with a saturation uptake of 688 g-L^-1 (1 bar, 195 K). The corresponding CH₄ uptake was measured as 165 V(STP)/V (20 bar, 293 K) and 189 V(STP/V) (35 bar, 293 K) with a maximum CH₄ uptake for NOTT-220a recorded at 20 bar and 195 K to be 287 V(STP)/V, while H₂ uptake of NOTT-220a at 20 bar, 77 K is 42 g-L^-1. These gas uptakes have been modelled by grand canonical Monte Carlo (GCMC) and density functional theory (DFT) calculations, which confirm the experimental data and give insights into the nature of the binding sites of CH₄ and CO₂ in this porous hybrid material. High density: The 3,6-connected material [Bi₂(L)_1.5(H₂O) ₂]·(DMF)_3.5·(H₂O)₃ (NOTT-220-solv; see figure; L=biphenyl-3,3′,5,5′-tetracarboxylate) shows a new framework topology with a {4·6²} ₂{4²·6⁵·8⁸}{6 ²·8} point symbol. The desolvated material NOTT-220a shows a maximum CH₄ uptake of 287 V(STP)/V at 20 bar, 195 K with a CO ₂ uptake of 688 g-L^-1 at 1 bar, 195 K.