A trace amount of acetylene (C2H2, 1%) removal from ethylene/acetylene mixture is crucial for the production of polymer-grade ethylene (C2H4), which is a highly challenging task and currently is mainly realized via highly energy-intensive technologies. Herein, we first report the highly efficient trapping of C2H2 from C2H2/C2H4 mixtures using two hexafluorogermanate (GeF62-, GeFSIX) anion-functionalized hybrid ultramicroporous materials, GeFSIX-2-Cu-i and GeFSIX-14-Cu-i (also termed ZU-32 and ZU-33), as novel adsorbents. These GeFSIX materials exhibit high thermal stability and tunable pore structures and have a high density of electronegative GeF62- anions decorated on the pore surface. ZU-32 with an aperture size of 4.5 angstrom exhibits preferential binding ability for C2H2 molecules and thus offers an excellent separation selectivity of 67 for the C2H2/C2H4 (1/99) mixture. ZU-33 with 4,4-azopyridine (azpy, 9.0 angstrom) as an organic linker exhibits a contracted pore window size with pyridine ring tilting of ca. 30 degrees, which could efficiently block C2H4 molecules but still permit C2H2 molecules trapping into the pore channels. The strong hydrogen-bonding interactions between GeF62- and C2H2 and cooperative van der Waals (vdW) interactions between organic linkers and C2H2 enable ZU-33 to exhibit a record high C2H2 volumetric uptake of 61.5 cm(3) cm(-3) at 0.01 bar and 298 K with separation selectivity over 1100 forC(2)H(2)/C2H4 (1/99) mixture. The actual separation performances of GeFSIX materials are evaluated by conducting experimental breakthrough tests. A total of 99.9999% C2H4 can be obtained from a C2H2/C2H4 (1/99) mixture by one-step column adsorption using GeFSIX materials as adsorbents with a C2H4 productivity up to 1662.1 mL g(-1). The binding sites of GeFSIX materials for C2H2 molecules were investigated by first-principles density functional theory (DFT) calculations. This work not only indicates that GeFSIX materials are lead candidates for the separation of C2H2/C2H4 mixture but also are attractive adsorbents for the separation of other gas mixtures containing acidic or polar gaseous components.