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The metal–organic frameworks M₂(m-dobdc) (M = Mn, Fe, Co, Ni; m-dobdc^4– = 4,6-dioxido-1,3-benzenedicarboxylate) were evaluated as adsorbents for separating olefins from paraffins. Using single-component and multicomponent equilibrium gas adsorption measurements, we show that the coordinatively unsaturated M²⁺ sites in these materials lead to superior performance for the physisorptive separation of ethylene from ethane and propylene from propane relative to any known adsorbent, including para-functionalized structural isomers of the type M₂(p-dobdc) (p-dobdc^4– = 2,5-dioxido-1,4-benzenedicarboxylate). Notably, the M₂(m-dobdc) frameworks all exhibit an increased affinity for olefins over paraffins relative to their corresponding structural isomers, with the Fe, Co, and Ni variants showing more than double the selectivity. Among these frameworks, Fe₂(m-dobdc) displays the highest ethylene/ethane …