Tuning Pore Polarization to Boost Ethane/Ethylene Separation Performance in Hydrogen-Bonded Organic Frameworks

Hydrogen-bonded organic frameworks (HOFs) show great potential in energy-saving C₂H₆/C₂H₄ separation, but there are few examples of one-step acquisition of C₂H₄ from C₂H₆/C₂H₄ because it is still difficult to achieve the reverse-order adsorption of C₂H₆ and C₂H₄. In this work, we boost the C₂H₆/C₂H₄ separation performance in two graphene-sheet-like HOFs by tuning pore polarization. Upon heating, an in situ solid phase transformation can be observed from HOF-NBDA(DMA) (DMA=dimethylamine cation) to HOF-NBDA , accompanied with transformation of the electronegative skeleton into neutral one. As a result, the pore surface of HOF-NBDA has become nonpolar, which is beneficial to selectively adsorbing C₂H₆. The difference in the capacities for C₂H₆ and C₂H₄ is 23.4 cm³ g⁻¹ for HOF-NBDA , and the C₂H₆/C₂H₄ uptake ratio is 136 %, which are much higher than those for HOF-NBDA(DMA) (5.0 cm³ g⁻¹ and 108 % respectively). Practical breakthrough experiments demonstrate HOF-NBDA could produce polymer-grade C₂H₄ from C₂H₆/C₂H₄ (1/99, v/v) mixture with a high productivity of 29.2 L kg⁻¹ at 298 K, which is about five times as high as HOF-NBDA(DMA) (5.4 L kg⁻¹). In addition, in situ breakthrough experiments and theoretical calculations indicate the pore surface of HOF-NBDA is beneficial to preferentially capture C₂H₆ and thus boosts selective separation of C₂H₆/C₂H₄.     

Scalable Synthesis of Robust MOF for Challenging Ethylene Purification and Propylene Recovery with Record Productivity

Ethylene (C₂H₄) purification and propylene (C₃H₆) recovery are highly relevant in polymer synthesis, yet developing physisorbents for these industrial separation faces the challenges of merging easy scalability, economic feasibility, high moisture stability with great separation efficiency. Herein, we reported a robust and scalable MOF (MAC-4) for simultaneous recovery of C₃H₆ and C₂H₄. Through creating nonpolar pores decorated by accessible N/O sites, MAC-4 displays top-tier uptakes and selectivities for C₂H₆ and C₃H₆ over C₂H₄ at ambient conditions. Molecular modelling combined with infrared spectroscopy revealed that C₂H₆ and C₃H₆ molecules were trapped in the framework with stronger contacts relative to C₂H₄. Breakthrough experiments demonstrated exceptional separation performance for binary C₂H₆/C₂H₄ and C₃H₆/C₂H₄ as well as ternary C₃H₆/C₂H₆/C₂H₄ mixtures, simultaneously affording record productivities of 27.4 and 36.2 L kg⁻¹ for high-purity C₂H₄ (≥99.9 %) and C₃H₆ (≥99.5 %). MAC-4 was facilely prepared at deckgram-scale under reflux condition within 3 hours, making it as a smart MOF to address challenging gas separations.     

New Dinuclear Ru2(CO)4 Sawhorse‐Type Complexes Containing Bridging Carboxylato Ligands

The thermal reaction of Ru₃(CO)₁₂ with ethacrynic acid, 4‐[bis(2‐chlorethyl)amino]benzenebutanoic acid (chlorambucil), or 4‐phenylbutyric acid in refluxing solvents, followed by addition of two‐electron donor ligands (L), gives the diruthenium complexes Ru₂(CO)₄(O₂CR)₂L₂ ( 1 : R = CH₂O‐C₆H₂Cl₂‐COC(CH₂)C₂H₅, L = C₅H₅N; 2 : R = CH₂O‐C₆H₂Cl₂‐COC(CH₂)C₂H₅, L = PPh₃; 3 : R = C₃H₆‐C₆H₄‐N(C₂H₄‐Cl)₂, L = C₅H₅N; 4 : R = C₃H₆‐C₆H₄‐N(C₂H₄‐Cl)₂, L = PPh₃; 5 : R = C₃H₆‐C₆H₅, L = C₅H₅N; 6 : R = C₃H₆‐C₆H₅, L = PPh₃). The single‐crystal structure analyses of 2 , 3 , 5 and 6 reveal a dinuclear Ru₂(CO)₄ sawhorse structure, the diruthenium backbone being bridged by the carboxylato ligands, while the two L ligands occupy the axial positions of the diruthenium unit.     

Active Sites Decorated Nonpolar Pore-Based MOF for One-step Acquisition of C2H4 and Recovery of C3H6

Herein, a 2-fold interpenetrated metal-organic framework (MOF) Zn-BPZ-TATB with accessible N/O active sites in nonpolar pore surfaces was reported for one-step C₂H₄ purification from C₂H₆ or C₃H₆ mixtures as well as recovery of C₃H₆ from C₂H₆/C₃H₆/C₂H₄ mixtures. The MOF exhibits the favorable C₂H₆ and C₃H₆ uptakes (>100 cm³ g⁻¹ at 298 K under 100 kPa) as well as selective adsorption of C₂H₆ and C₃H₆ over C₂H₄. The C₃H₆- and C₂H₆-selective feature were investigated detailedly by experimental tests as well as sorption kinetic studyies. Molecular modelling revealed the multiple interactions between C₃H₆ or C₂H₆ molecules and methyl groups as well as triazine rings in pores. Zn-BPZ-TATB not only can directly generate 323.4 L kg⁻¹ and 15.4 L kg⁻¹ of high-purity (≥99.9 %) C₂H₄ from C₃H₆/C₂H₄ and C₂H₆/C₂H₄ mixtures, but also provide a large high-purity (≥99.5 %) C₃H₆ recovery capacity of 60.1 L kg⁻¹ from C₃H₆/C₂H₄ mixtures. More importantly, the high-purity C₃H₆ (≥99.5 %) and C₂H₄ (≥99.9 %) with the productivities of 38.2 and 12.7 L kg⁻¹ can be simultaneously obtained from C₂H₆/C₃H₆/C₂H₄ mixtures through a single adsorption/desorption cycle.     

Copolymerization of trans-2,6-diazido-hexaphenylcyclophosphonitrile tetramer with 1,4-bis(diphenylphosphino)butane or 4,4′-bis(diphenylphosphino)biphenyl

Polymers [N(PN)₄(C₆H₅)₆N?P(C₆H₅)₂(CH₂)₄P(C₆H₅)₂]_x and [N(PN)₄(C₆H₅)₆N?P–(C₆H₅)₂C₆H₄C₆H₄P(C₆H₅)₂]_x have been formed by thermal copolymerization of trans-2,6-diazidohexaphenylcyclophosphonitrile [N₃(PN)₄(C₆H₅)₆N₃] with either 1,4-bis-(diphenylphosphino)butane [(C₆H₅)₂P(CH₂)₄P(C₆H₅)₂] or 4,4′-bis(diphenylphosphino)-biphenyl [(C₆H₅)₂C₆H₄C₆H₄P(C₆H₅)₂]. The maximum molecular weights obtained were about 10,000. A polymer endcapped with triphenyl phosphine was stable to 400°C.     

Control of pore environment in highly porous carbon materials for C2H6/C2H4 separation with exceptional ethane uptake

Adsorptive separation of C₂H₆ from C₂H₄ by adsorbents is an energy-efficient and promising method to boost the polymer grades C₂H₄ production. However, that C₂H₆ and C₂H₄ display very similar physical properties, making their separation extremely challenging. In this work, by regulating the pore environment in a family of chitosan-based carbon materials (C-CTS-1, C-CTS-2, C-CTS-4, and C-CTS-6)- we target ultrahigh C₂H₆ uptake and C₂H₆/C₂H₄ separation, which exceeds most benchmark carbon materials. Explicitly, the C₂H₆ uptake of C-CTS-2 (166 cm³/g at 100 kPa and 298 K) has the second-highest adsorption capacity among all the porous materials. In addition, C-CTS-2 gives C₂H₆/C₂H₄ selectivity of 1.75 toward a 1:15 mixture of C₂H₆/C₂H₄. Notably, the adsorption enthalpies for C₂H₆ in C-CTS-2 are low (21.3 kJ/mol), which will facilitate regeneration in mild conditions. Furthermore, C₂H₆/C₂H₄ separation performance was confirmed by binary breakthrough experiments. Under different ethane/ethylene ratios, C-CTS-X extracts a low ethane concentration from an ethane/ethylene mixture and produces high-purity C₂H₄ in one step. Spectroscopic measurement and diffraction analysis provide critical insight into the adsorption/separation mechanism. The nitrogen functional groups on the surface play a vital role in improving C₂H₆/C₂H₄ selectivity, and the adsorption capacities depend on the pore size and micropore volume. Moreover, these robust porous materials exhibit outstanding stability (up to 800 °C) and can be easily prepared on a large scale (kg) at a low cost (～$26 per kg), which is very significant for potential industrial applications.     

Highly Robust Microporous Metal-Organic Frameworks for Efficient Ethylene Purification under Dry and Humid Conditions

Two C₂H₆-selective metal-organic framework (MOF) adsorbents with ultrahigh stability, high surface areas, and suitable pore size have been designed and synthesized for one-step separation of ethane/ethylene (C₂H₆/C₂H₄) under humid conditions to produce polymer-grade pure C₂H₄. Experimental results reveal that these two MOFs not only adsorb a high amount of C₂H₆ but also display good C₂H₆/C₂H₄ selectivity verified by fixed bed column breakthrough experiments. Most importantly, the good water stability and hydrophobic pore environments make these two MOFs capable of efficiently separating C₂H₆/C₂H₄ under humid conditions, exhibiting the benchmark performance among all reported adsorbents for separation of C₂H₆/C₂H₄ under humid conditions. Moreover, the affinity sites and their static adsorption energies were successfully revealed by single crystal data and computation studies. Adsorbents described in this work can be used to address major chemical industrial challenges.     

Synthesis and electrochemical studies of organometallic cobalt(III) complexes with substituted benzonitrile chromophores: NMR spectroscopic data as a probe on the second-order non-linear optical properties

The family of organometallic Co(III) benzonitrile derivatives of general formula [CoCp(dppe)(p-NCR)][PF₆]₂ (R = C₆H₄NMe₂, C₆H₄NH₂, C₆H₄OMe, C₆H₄C₆H₅, C₆H₅, C₆H₄C₆H₄NO₂, and C₆H₄NO₂) have been synthesized. Spectroscopic and electrochemical data were analyzed in order to evaluate the extent of electronic coupling between the organometallic fragment and the nitrile ligands. An attempt of correlation between NMR spectroscopic data and the second-order non-linear optical properties is presented, based on this work and available published data for related η⁵-monocyclopentadienyliron, ruthenium and nickel complexes.     

Acid-catalyzed polycondensation of bisdiazoalkanes

Dimerization reactions of diphenyldiazomethane have been applied to the polycondensation of six bisdiazobenzyl arylenes, namely 1,4- and 1,3-bis(α-diazobenzyl)-benzenes C₆H₅CN₂? (C₆H₄)? CN₂C₆H₅; 1,4- and 1,3-bis(α-diazo-p-methoxybenzyl)-benzenes, p,p′-MeO? C₆H₄? CN₂? (C₆H₄)? CN₂C₆H₄? OMe; 4,4′-bis(α-diazobenzyl)-diphenylmethane, C₆H₅CN₂? (C₆H₄CH₂C₆H₄)? CN₂C₆H₅; and 4,4′-bis(α-diazobenyl)-diphenyl ether, C₆H₅CN₂? (C₆H₄? O? C₆H₄)CN₂C₆H₅. Depending on the nature of the catalysts, polyene-arylenes (? C(Ar)?C(Ar)? C₆H₄)_n, and polyazine-arylenes, (? C(Ar)?N? N? C(Ar)? C₆H₄? )_n, can be obtained selectively by acid-catalyzed decomposition of these bisdiazoalkanes at room temperature. With perchloric acid and with arylsulfonic acids in strong polar media, polyene-arylenes are formed. On the other hand, boron trifluoride and arylsulfonic acids in solvents of low dielectric constant afford polyazine-arylenes. Less selective is the thermal decomposition at 75°C in toluene solution; it gives a polymer containing about 90% azine and 10% olefinic groups. All these polymers are soluble in common solvents. Their molecular weight vary from 3 200 to 5 000, i.e., X?_n from 12 to 20. The polyene-arylenes are very stable and decompose only around 500°C; the polyazine-arylenes are less stable and decompose around 370°C by losing nitrogen.     

通过核独立化学位移(NICS)计算研究二价三、五、七元环C2H2M, C4H4M and C6H6M(M=C, Si, Ge, Sn and Pb)的芳香族特性

The aromatic character of divalent three, five and seven-membered rings C₂H₂M, C₄H₄M and C₆H₆M(M=C, Si, Ge, Sn and Pb) is investigated through magnetic and geometric criteria by Density Functional Theory (DFT)method using 6^-311++G(3df,2p) basis set of the GAUSSIAN 98 program. The result of Nucleus-independent Chemical Shifts (NICS)(0.5) calculations show an aromatic character for singlet state of C₂H₂M(M=C, Si, Ge, Sn and Sn) and nonaromatic character for triplet states of C₂H₂M(except M=Ge and Pb). NICS (0.5) calculations show nonaromatic character for the singlet state of C₄H₄C and antiaromatic character for C₄H₄M(M=Si, Ge, Sn and Pb). In contrast, NICS (0.5) calculations indicate antiaromatic character for the triplet state of C₄H₄C and nonaromatic character to C₄H₄M(M=Si, Ge, Sn and Pb). NICS (0.5) calculations show a slightly homoaromatic character for the singlet state of C₆H₆M and anti-aromatic character for triplet state of C₆H₆M.     

Long‐Lived Radical Cation Salts Obtained by Interaction of Monocyclic Arenes with Niobium and Tantalum Pentahalides at Room Temperature: EPR and DFT Studies

The 1:3 reactions of the alkoxy arenes 1,4‐(MeO)₂C₆H₄ and 1,4‐F₂‐2,5‐(MeO)₂C₆H₂ with TaF₅ in chloroform at 40–50 °C resulted in formation in about 35 % yield of the long‐lived radical cation salts [1,4‐(MeO)₂C₆H₄][Ta₂F₁₁] ( 2 a ) and [1,4‐F₂‐2,5‐(MeO)₂C₆H₂][Ta₂F₁₁] ( 2 b ), respectively. The non‐alkoxy‐substituted [arene][M₂X₁₁] [M=Ta, X=F: arene=C₆H₅Me ( 2 c ), 1,4‐C₆H₄Me₂ ( 2 d ), C₆H₅F ( 2 e ), C₆H₅NO₂ ( 2 f ); M=Nb, X=F: arene=C₆H₅Me ( 4 a ), 1,4‐C₆H₄Me₂ ( 4 b ), C₆H₅F ( 4 c ), C₆H₅NO₂ ( 4 d ); M=Ta, X=Cl: arene=1,4‐C₆H₄Me₂ ( 5 )] were obtained from the 3:1 reactions of MX₅ with the appropriate arene in chloroform at temperatures in the range 40–90 °C. Compounds 2 – 5 were detected by EPR spectroscopy (in CHCl₃) at room temperature, and their gas‐phase structures were optimized by DFT calculations. Formation of the M^IV species [MX₄(NCMe)₂] [M=Ta, X=F ( 3 a ); M=Nb, X=F ( 3 b ); M=Ta, X=Cl ( 3 c )] was ascertained by EPR spectroscopy on solutions obtained by treatment of the reaction mixtures with acetonitrile. Non‐selective reactions occurred upon combination of 1,4‐F₂‐2,5‐(MeO)₂C₆H₂ with AgNbF₆ (in CH₂Cl₂) and 1,4‐(MeO)₂C₆H₄ with SbF₅.     

Facilitated Transport of C<Subscript>2</Subscript>H<Subscript>4</Subscript> in a SiO<Subscript>2</Subscript>-poly(N-vinylpyrrolidone)-Ag<Superscript>+</Superscript> Inorganic-Organic Hybrid Membrane

Inorganic-organic hybrid membranes containing silica as the structure matrix, poly(N-vinylpyrrolidone) (PVP) as the organic mediating agent and silver ions as olefinic carriers were prepared using sol–gel method and dip-coating process. The structure and permeances of the membranes for N₂, He, C₂H₄, C₂H₆ at different temperatures indicated that defect-free membranes were obtained and the transportation of the C₂H₄ through the membranes followed the dissolution and diffusion mechanism. Ideal separation factors of C₂H₄/C₂H₆ through the membranes were evaluated at the temperature of 298, 373 and 423 K respectively using mixture gas of 50% C₂H₄-50% C₂H₆. The results showed that the ideal separation factors of C₂H₄/C₂H₆ through the membranes were obviously greater than the ratio of PC₂H₄/PC₂H₆ obtained from the single gas measurement due to the hindering effect by the adsorbed C₂H₄. The ideal separation factors of C₂H₄/C₂H₆ increased with temperature and reached 10 at 423 K, which suggested that C₂H₄ and C₂H₆ could be separated at lower humidity compared to the reported organic polymer/silver salt membranes in which humidified gases and higher silver loading were usually used. The transport of C₂H₄ in the inorganic-organic hybrid membrane was proposed to follow the hopping mechanism, that is, olefins moved across the fixed silver sites.     

Komplexe der Alkalimetalltetraphenylborate mit makrocyclischen Kronenethern

Complexes of the Alkali Metal Tetraphenylborates with Macrocyclic Crown Ethers Alkali metal tetraphenylborates, MB(C₆H₅)₄ (M = Li to Cs), react in tetrahydrofuran with macrocyclic crown ethers to give complexes of the general formula MB(C₆H₅)₄(crown)_m(THF)_n. Suitable single crystals for X‐ray structure analysis were grown from a solvent mixture of tetrahydrofuran and n‐hexane. The salt like complexes [Li(12‐crown‐4)(thf)][B(C₆H₅)₄] ( 1 ), [Na(15‐crown‐5)(thf)][B(C₆H₅)₄] ( 2 ), and [Cs(18‐crown‐6)₂][B(C₆H₅)₄] · THF ( 6 ), the mononuclear molecular complexes [KB(C₆H₅)₄(18‐crown‐6)(thf)] ( 3 ), [RbB(C₆H₅)₄(18‐crown‐6)] ( 4 ), and [CsB(C₆H₅)₄(18‐crown‐6)] · THF ( 5 ), and the compound [CsB(C₆H₅)₄(18‐crown‐6)]₂[Cs(18‐crown‐6)₂][B(C₆H₅)₄] ( 7 ), which contains a binuclear molecule ([CsB(C₆H₅)₄(18‐crown‐6)]₂) beside a [Cs(18‐crown‐6)₂]⁺ cation and a [B(C₆H₅)₄]^? anion, are described. All compounds are charactarized by infrared spectra, elemental analysis, NMR‐spectroscopy, and X‐ray single crystal structure analysis.     

Zur Wechselwirkung einiger Übergangsmetallhalogenide mit o-Mercaptophenol

The interaction of some transition metal halides with o-mercaptophenol o-Mercaptophenol reacts with WCl₆, TiCl₄, ZrCl₄, NbCl₅ and TaCl₅ giving the corresponding tris-chelat-komplexe W(C₆H₄OS)₃, H₂[M(C₆H₄OS)₃] (M = Ti, Zr), H[M(C₆H₄OS)₃] (M = Nb, Ta). (C₅H₅)₂TiCl₂ and (C₅H₅)₂ZrBr₂give in presence of triethylamine the compounds (C₅H₅)₂M(C₆H₄OS) (M = Ti, Zr). By reaction of nickel(II) acetyl-acetonate with o-mercaptophenol the polymeric octahedral complex nickel-bis-(o-hydroxy-thiophenolate) results.     

A Microporous Metal-Organic Framework with Unique Aromatic Pore Surfaces for High Performance C2H6/C2H4 Separation

Developing adsorptive separation processes based on C₂H₆-selective sorbents to replace energy-intensive cryogenic distillation is a promising alternative for C₂H₄ purification from C₂H₄/C₂H₆ mixtures, which however remains challenging. During our studies on two isostructural metal–organic frameworks ( Ni-MOF 1 and Ni-MOF 2 ), we found that Ni-MOF 2 exhibited significantly higher performance for C₂H₆/C₂H₄ separation than Ni-MOF-1 , as clearly established by gas sorption isotherms and breakthrough experiments. Density-Functional Theory (DFT) studies showed that the unblocked unique aromatic pore surfaces within Ni-MOF 2 induce more and stronger C−H⋅⋅⋅π with C₂H₆ over C₂H₄ while the suitable pore spaces enforce its high C₂H₆ uptake capacity, featuring Ni-MOF 2 as one of the best porous materials for this very important gas separation. It generates 12 L kg⁻¹ of polymer-grade C₂H₄ product from equimolar C₂H₆/C₂H₄ mixtures at ambient conditions.     

A novel and practical synthetic method of 3(2H)-furanone derivatives

A novel, convenient synthetic method of 5-atyl-2,2-dimethyl-3(2H)-furanones (aryl = C₆H₅, 2-CH₃C₆H₄, 3-CH₃C₆H₄, 4-CH₃C₆H₄, 2-CIC₆H₄, 4-CIC₆H₄, 2,4-Cl₂C₆H₃) is described. It involves the Claisen-Schmidt condensation (potassium hydroxide/ethanol) of aromatic aldehydes with 3-hydroxy-3-methyl-2-butanone to give enones, whose bromination followed by alkaline hydrolysis (sodium hydroxide/ethanol) affords 3(2H)-furanone derivatives in 54–64% overall yields. The procedure is also applicable to nicotinaldehyde and furfural, although the yields are not satisfactory.     

Cumulative author index

For the compounds C₆H₅C₆H₄YC₆H₄C₆H₅ and C₆H₅C₆H₄YC₆H₄C₆H₄YC₆H₄C₆H₅ where Y is either Si(CH₃)₂ or CH₂, reduction potentials and p-band positions are reported. These data as well as the UV data for several phenyl derivatives are consistent with silicon blocking, to a large extent, conjugation (little or no through conjugation) of biphenyl moieties separated by Si(CH₃)₂groups.     

Synthesis and characterisation of cyclo-boratetrasiloxane, (RBO)(Me2SiO)3 (R=nBu,Ar), derivatives

Low temperature reactions of dilute solutions of 1,5-dichloro-1,1,3,3,5,5-hexamethyltrisiloxane with boronic acids {RB(OH)₂; R=ⁿBu, C₆H₄Me-2, C₆H₄Me-3, C₆H₄Me-4, C₆H₄OMe-3, C₆H₄OMe-4, C₆H₄Br-2, C₆H₄Br-3, C₆H₄Br-4} in the presence of a twofold excess of Et₃N afforded the 8-membered ring products, cyclo-boratetrasiloxanes, (RBO)(Me₂SiO)₃, in moderate yields. New compounds were colourless oils and were characterised by elemental analysis, NMR (¹H, ¹¹B, ¹³C, ²⁹Si), IR and MS. The cyclo-boratetrasiloxanes are weakly Lewis acidic, with acceptor number (AN) values of ∼30, but do not form adducts with amines.     

Ab initio quantum-chemical calculations of interactions of ions and hydrides of alkali metals with C3H6 and C4H8 molecules

Calculations of the C₃H₆ · LiH, C₄H₈ · M⁺, and C₄H₈ · MH systems and of C₂H₂ · MH complexes (M = Li or Na) were carried out by the unrestricted Hartree-Fock-Roothaan (UHF) method with partial optimization of the geometry using fixed geometric parameters of the C₃H₆ and C₄H₈ molecules. The standard 3-21G and 6-31G* basis sets were used. Unlike the C₃H₆ · LiH structure, the C₄H₈ · M⁺ and C₄H₈ · MH systems are typical complexes. It was found that the C₄H₈ · M⁺, C₄H₈ · MH, and C₂H₂ · MH complexes are similar in coordination of M⁺ ions and MH molecules by carbon atoms in spite of considerable differences in the interatomic distances (–1 A) between these atoms in the C₄H₈ and C₂H₂ molecules. The heats of formation (Q), which were calculated in the UHF/6-31G* approximation and using second- and fourth-order Möller-Plesset perturbation theory taking into account the electron correlation energy in the MP2/6-31G*. MP4(SDQ)/6-31G*, and MP4(SDTQ)/6-31G* approximations, satisfy the following relationships: Q(C₂H₃ · MH) < Q(C₄H₈ · MH) < Q(C₄H₈ · M⁺). It was observed that in going from Li to Na the corresponding values of Q tend to decrease.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 7, pp. 1636–1640, July, 1996.     

Spatial Distribution of Nitrogen Binding Sites in Metal-Organic Frameworks for Selective Ethane Adsorption and One-Step Ethylene Purification

The one-step purification of ethylene (C₂H₄) from mixtures containing ethane (C₂H₆) and acetylene (C₂H₂) is an industrially important yet challenging process. In this work, we present a site-engineering strategy aimed at manipulating the spatial distribution of binding sites within a confined pore space. We realized successfully by incorporating nitrogen-containing heterocycles, such as indole-5-carboxylic acid (Ind), benzimidazole-5-carboxylic acid (Bzz), and indazole-5-carboxylic acid (Izo), into the robust MOF-808 platform via post-synthetic modification. The resulting functionalized materials, namely MOF-808-Ind, MOF-808-Bzz, and MOF-808-Izo, demonstrated significantly improved selectivity for C₂H₂ and C₂H₆ over C₂H₄. MOF-808-Bzz with two uniformly distributed nitrogen binding sites gave the optimal geometry for selective ethane trapping through multiple strong C−H⋅⋅⋅N hydrogen bonds, leading to the highest C₂H₂/C₂H₄ and C₂H₆/C₂H₄ combined selectivities among known MOFs. Column breakthrough experiments validated its ability to purify C₂H₄ from ternary C₂H₂/C₂H₄/C₂H₆ mixtures in a single step.