Selective Gas Uptake and Rotational Dynamics in a (3,24)-Connected Metal–Organic Framework Material

The desolvated (3,24)-connected metal–organic framework (MOF) material, MFM-160a, [Cu3(L)(H2O)3] [H6L = 1,3,5-triazine-2,4,6-tris(aminophenyl-4-isophthalic acid)], exhibits excellent high-pressure uptake of CO2 (110 wt% at 20 bar, 298 K) and highly selective separation C2 hydrocarbons from CH4 1 bar pressure. Henry’s law selectivities 79:1 for C2H2:CH4 70:1 C2H4:CH4 K are observed, consistent with ideal adsorption solution theory (IAST) predictions. Significantly, MFM-160a shows a selectivity 16:1 C2H2:CO2. Solid-state 2H NMR spectroscopic studies on partially deuterated MFM-160-d12 confirm an ultra-low barrier (∼2 kJ mol–1) to rotation the phenyl group in activated MOF rate 5 orders magnitude slower than usually observed solid-state materials (1.4 × 106 Hz cf. 1011–1013 Hz). Upon introduction or C2H2 into this was found increase increasing gas pressure, phenomenon attributed weakening intramolecular hydrogen bond triazine-containing linker upon binding. DFT calculations binding energies interactions around triazine core entirely observations.