Separation of ternary gas mixtures is challenging and has rarely been achieved with a single porous solid material. Herein a trinuclear iron(III) based metal–organic framework (MOF) with high water stability, {[Fe₃(μ₃-O)(DFBDC)₃(TPT)](OH)}_n (JXNU-14) (DFBDC²⁻ = 2,5-difluoroterephthalate and TPT = 2,4,6-tri(4-pyridinyl)-1,3,5-triazine), is applied for the removal of CO₂ from a ternary C₂H₂/C₂H₄/CO₂ mixture. The trigonal bipyramidal cavities and cylindrical cavities decorated with highly electronegative fluorine and oxygen atoms and abundant π rings in JXNU-14 offer stronger affinity for C₂H₂ and C₂H₄ than for CO₂, resulting in the high-performance separation of a ternary equimolar mixture of C₂H₂, C₂H₄, and CO₂, which is demonstrated by pure-component gas adsorption isotherms and actual column breakthrough experiments. The much stronger binding of C₂H₂ and C₂H₄ as compared to CO₂ was further revealed by computational simulations. This work provides a useful strategy for the construction of MOFs possessing high-density electronegative sites for the efficient removal of CO₂ from a ternary C₂H₂/C₂H₄/CO₂ mixture.