Construction of Negative Electrostatic Pore Environments in a Scalable,Stable and Low-Cost Metal-organic Framework for One-Step Ethylene Purification from Ternary Mixtures

One-step separation of C₂H₄ from ternary C₂ mixtures by physisorbents remains a challenge to combine excellent separation performance with high stability, low cost, and easy scalability for industrial applications. Herein, we report a strategy of constructing negative electrostatic pore environments in a stable, low-cost, and easily scaled-up aluminum MOF (MOF-303) for efficient one-step C₂H₂/C₂H₆/C₂H₄ separation. This material exhibits not only record high C₂H₂ and C₂H₆ uptakes, but also top-tier C₂H₂/C₂H₄ and C₂H₆/C₂H₄ selectivities at ambient conditions. Theoretical calculations combined with in situ infrared spectroscopy indicate that multiple N/O sites on pore channels can build a negative electro-environment to provide stronger interactions with C₂H₂ and C₂H₆ over C₂H₄. Breakthrough experiments confirm its exceptional separation performance for ternary mixtures, affording one of the highest C₂H₄ productivity of 1.35 mmol g⁻¹. This material is highly stable and can be easily synthesized at kilogram-scale from cheap raw materials using a water-based green synthesis. The benchmark combination of excellent separation properties with high stability and low cost in scalable MOF-303 has unlocked its great potential in this challenging industrial separation.     

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.     

Basicity of bisperhalophenyl aurates toward closed-shell metal ions: metallophilicity and additional interactions

The interaction of bisperhalophenyl aurates [AuR₂]^? (R?=?C₆F₅, C₆F₃Cl₂, and C₆Cl₅) with the closed-shell Ag⁺, Cu⁺, and Tl⁺ ions has been studied theoretically and compared with the experimentally known X-ray diffraction crystal structures. Initially, the aurates have been fully optimized at MP2 level of theory in a D _2h symmetry. The analysis of the basicity of the three aurates [AuR₂]^? (R?=?C₆F₅, C₆F₃Cl₂ and C₆Cl₅) against Ag⁺ ions in a C _2v symmetry has been calculated in point-by-point bsse-corrected interaction energy analysis at HF and MP2 levels of theory. Taking into account the experimental observation of additional interactions between the heterometals and C _ipso atoms at the perhalophenyl rings or halogen atoms at the ortho position of the perhalophenyl rings, dinuclear models of the type [AuR₂]^?···Ag⁺ (R?=?C₆Cl₅, and C₆F₅); [AuR₂]^?···Cu⁺ (R?=?C₆F₅, and C₆Cl₅) and [AuR₂]^?···Tl⁺ (R?=?C₆F₅, and C₆Cl₅) with a C _2v , C ₂ , and C _s symmetries have been optimized at DFT-B3LYP level. The interaction energies have been computed through bsse-corrected single point HF and MP2 calculations. The energy stabilization provided and the heterometal preference have been analyzed and compared with the experimental results.     

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.     

Observations on the reactivity of tris(tetramethylethylenedioxyboryl)methide ion

Treatment of tetrakis(tetramethylethylenedioxyboryl)methane, (Me₄C₂ - O₂B)₄C, in THF with butyllithium at ?78° generates the tris(tetramethylethylenedioxyboryl)methide ion, (Me₄C₂O₂B)₃C^?, which reacts with chlorotrimethylsilane at ?78° to form trichlorosilyltris(tetramethylethylenedioxyboryl)-methane, (Me₄C₂O₂B)₃CSiMe₃. The yield was low, but other attempts to form silyltriborylmethanes have failed altogether. The ion (Me₄C₂O₂B)₃C^? reacts with tetraphenylcyclopentadienone at ?78° to form the expected fulvene, 1,1-bis-(tetramethylethylenedioxyboryl)-2,3,4,5-tetraphenylfulvene. The red color of the tetraphenylcyclopentadienone is converted immediately to the brown of the fulvene product, indicating that the β-elimination of boron and oxygen occurs rapidly under basic conditions at ?78°.     

Molecular Sieving of Acetylene from Ethylene in a Rigid Ultra-microporous Metal Organic Framework.

Rigid molecular sieving materials are the ideal candidates for gas separation (e. g., C₂H₂/C₂H₄) due to their ultrahigh adsorption selectivity and the absence of gas co-adsorption. However, the absolute molecular sieving effect for C₂H₂/C₂H₄ separation has rarely been realized because of their similar physicochemical properties. Herein, we demonstrate the absolute molecular sieving of C₂H₂ from C₂H₄ by a rigid ultra-microporous metal-organic framework ( F−PYMO−Cu ) with 1D regular channels (pore size of ca. 3.4 Å). F−PYMO−Cu exhibited moderate acetylene uptake (35.5 cm³/cm³), but very low ethylene uptake (0.55 cm³/cm³) at 298 K and 1 bar, yielding the second highest C₂H₂/C₂H₄ uptake ratio of 63.6 up to now. One-step C₂H₄ production from a binary mixture of C₂H₂/C₂H₄ and a ternary mixture of C₂H₂/CO₂/C₂H₄ at 298 K was achieved and verified by dynamic breakthrough experiments. Coupled with excellent thermal and water stability, F−PYMO−Cu could be a promising candidate for industrial C₂ separation tasks.     

Low-Concentration C2H6 Capture Enabled by Size Matching in the Ultramicropore

Low-concentration ethane capture is crucial for environmental protection and natural gas purification. The ideal physisorbent with strong C₂H₆ interaction and large C₂H₆ uptake at low-concentration level has rarely been reported, due to the large pK_a value and small quadrupole moment of C₂H₆. Herein, we demonstrate the perfectly size matching between the ultramicropore (pore size of 4.6 Å) and ethane (kinetic diameter of 4.4 Å) in a nickel pyridine-4-carboxylate metal–organic framework (IISERP-MOF 2 ), which enables the record-breaking performance for low concentration C₂H₆ capture. IISERP-MOF 2 exhibits the large C₂H₆ adsorption enthalpy of 56.7 kJ/mol, and record-high C₂H₆ uptake at low pressure of 0.01–0.1 bar and 298 K (1.8 mmol/g at 0.01 bar). Molecule simulations and C₂H₆-loading crystal structure analysis revealed that the maximized interaction sites in IISERP-MOF 2 with ethane molecule originates the strong C₂H₆ adsorption. The dynamic breakthrough experiments for gas mixtures of C₂H₆/N₂(1/999, v/v) and C₂H₆/CH₄ (5/95, v/v) proved the excellent low-concentration C₂H₆ capture performance.     

Overcoming the Trade-Off between C2H2 Sorption and Separation Performance by Regulating Metal-Alkyne Chemical Interaction in Metal-Organic Frameworks

Designing porous materials for C₂H₂ purification and safe storage is essential research for industrial utilization. We emphatically regulate the metal-alkyne interaction of Pd^II and Pt^II on C₂H₂ sorption and C₂H₂/CO₂ separation in two isostructural NbO metal–organic frameworks (MOFs), Pd/Cu-PDA and Pt/Cu-PDA . The experimental investigations and systematic theoretical calculations reveal that Pd^II in Pd/Cu-PDA undergoes spontaneous chemical reaction with C₂H₂, leading to irreversible structural collapse and loss of C₂H₂/CO₂ sorption and separation. Contrarily, Pt^II in Pt/Cu-PDA shows strong di-σ bond interaction with C₂H₂ to form specific π-complexation, contributing to high C₂H₂ capture (28.7 cm³ g⁻¹ at 0.01 bar and 153 cm³ g⁻¹ at 1 bar). The reusable Pt/Cu-PDA efficiently separates C₂H₂ from C₂H₂/CO₂ mixtures with satisfying selectivity and C₂H₂ capacity (37 min g⁻¹). This research provides valuable insight into designing high-performance MOFs for gas sorption and separation.     

Reactions of C2(a 3πu) with CH4, C2H2, C2H4, C2H6, and O2 using multiphoton UV excimer laser photolysis

C₂(a ³π_u) disappearance rate constants of 1.44, 0.96, 0.0296, 0.0130 and < 10^?6(x10^?10cm³s^?1) are reported for reactions with C₂H₄, C₂H₂, O₂, C₂H₆, and CH₄, respectively at 298 K. C₂(a ³π_u) fragments are generated by multiphoton ArF excimer laser photodissociation at C₂H₂, and monitored by dye laser induced fluorescence. Arguments are presented which favor chemical reactions over the C₂(a ³π_u) → (X ¹σ⁺_g) quenching channel. C₂ + C₂H₂ represents the one possible exception to the reactive channel.     

The protonation of Co(C5Me4Et)(C2H4)2

Reversible protonation of the bis-ethylene complex, Co(C₅Me₄Et)(C₂H₄)₂ yields [Co(C₅Me₄Et)(C₂H₄)₂H][BF₄], which readily exchanges its hydridic and olefinic protons stereospecifically at low temperatures; subsequent protonation at room temperature yields cobalt(III) complexes, C₂H₄ and C₂H₆.     

Rate constant and RRKM product study for the reaction between CH3 and C2H3 at T = 298 K

The total rate constant k₁ has been determined at P = 1 Torr nominal pressure (He) and at T = 298 K for the vinyl‐methyl cross‐radical reaction: (1) CH₃ + C₂H₃ → Products. The measurements were performed in a discharge flow system coupled with collision‐free sampling to a mass spectrometer operated at low electron energies. Vinyl and methyl radicals were generated by the reactions of F with C₂H₄ and CH₄, respectively. The kinetic studies were performed by monitoring the decay of C₂H₃ with methyl in excess, 6 < [CH₃]₀/ [C₂H₃]₀ < 21. The overall rate coefficient was determined to be k₁(298 K) = (1.02 ± 0.53) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ with the quoted uncertainty representing total errors. Numerical modeling was required to correct for secondary vinyl consumption by reactions such as C₂H₃ + H and C₂H₃ + C₂H₃. The present result for k₁ at T = 298 K is compared to two previous studies at high pressure (100–300 Torr He) and to a very recent study at low pressure (0.9–3.7 Torr He). Comparison is also made with the rate constant for the similar reaction CH₃ + C₂H₅ and with a value for k₁ estimated by the geometric mean rule employing values for k(CH₃ + CH₃) and k(C₂H₃ + C₂H₃). Qualitative product studies at T = 298 K and 200 K indicated formation of C₃H₆, C₂H₂, and C₃H₅ as products of the combination‐stabilization, disproportionation, and combination‐decomposition channels, respectively, of the CH₃ + C₂H₃ reaction. We also observed the secondary C₄H₈ product of the subsequent reaction of C₃H₅ with excess CH₃; this observation provides convincing evidence for the combination‐decomposition channel yielding C₃H₅ + H. RRKM calculations with helium as the deactivator support the present and very recent experimental observations that allylic C‐H bond rupture is an important path in the combination reaction. The pressure and temperature dependencies of the branching fractions are also predicted. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 304–316, 2000     

The equilibrium geometry,electronic structure and heat of formation of ortho-benzyne

Ab initio calculations at the SCF and Cl level have been carried out for the singlet ground state of ortho-benzyne (1,2,-dehydrobenzene) at a variety of C_2v molecular geometries. The principal features of the equilibrium geometry are: (1) an “acetylenic” C₁C₂ bond (1.22 Å): (2) a C₄C₅ bond slightly elongated (1.42 Å) with respect to benzene; (3) no elongation of the C₂C₃ and C₁C₆ bonds, due to the high s-character and angular deviation of the hybrid orbitals. Extended basis SCF calculations lead to an estimate of ≈ 120 kcal/mole for the ΔH^298°_f of o-benzyne.     

Hydration behavior of C2S and C2AS nanomaterials, synthetized by sol–gel method

Hydration behavior of dicalcium silicate (C₂S) (Cement chemistry nomenclature is used where C=CaO, S=SiO₂, A=Al₂O₃, S=SO₃) and gehlenite (C₂AS), synthesized by sol–gel method was investigated by means of isothermal heat flow calorimeter at different temperatures. These phases were obtained by crystallization processing at different temperatures from their xerogels (nano-crystalline) prepared by the sol–gel method at ambient temperature. The crystallization of C₂S begins below 600°C and it is well crystallized at 900°C. X-ray diffraction patterns reveal that β-C₂S is formed and it remains stable since after slow cooling. The crystallization of C₂AS xerogels starts with the formation of C₂S, then it reacts with alumina to form mineral C₂AS at 1100°C. The effect of hydration temperature upon the hydration reaction of C₂S obtained at 600 and 900°C and C₂AS annealed at 600 and 1100°C was investigated by means of isothermal calorimeter. An increase in the temperature of hydration brought about initial acceleration of all samples, as indicated by the increased magnitude of peak of calorimetric curves. The microstructure of the samples cured at hydrothermal condition after 1 and 7 days has been examined by means of scanning electron microscopy (SEM). Fine crystals of calcium silicate hydrate (C–S–H) were developed in C₂S samples, while C₂AS has been hydrated to form gehlenite hydrate supplemented by C–S–H.     

C74(BN)2的UV和IR 光谱研究

Equilibrium geometries of 16 possible isomers for C74（BN）2 were studied by INDO series of methods, to indicate that the most stable three geometries are those where boron and nitrogen atoms substitute carbon atoms located at the same hexagon near the longest axis of C78 （C2v） to form B-N-B-N unit. Electronic spectra of C74（BN）2 were investigated with INDO/CIS method. The reason for the red shift of UV absorptions for C74（BN）2 compared with those of C78 （C2v） was discussed. IR spectra for 9,8,28,29-C74（BN）2 and 28,29,30,31-C74（BN）2 were calculated on the basis of AM1 geometries.     

Selective formation of C60F18(g) and C60F36(g) by reaction of [60]fullerene with molecular fluorine

Fluorination of C₆₀(s), C₆₀(s)-MnF₂(s), C₆₀(s)-NiF₂(s) and C₆₀(s)-MnF₃(s) mixtures has been studied by Knudsen cell mass spectrometry with admission of molecular fluorine. The fluorination is selective when fullerene reacts with the fluorine chemisorbed on the MnF₂ surface. When the MnF₂ content in the initial mixture is at least 90 mol% both C₆₀F₁₈ and C₆₀F₃₆ are selectively formed. Under certain conditions, mixtures predominantly containing one of three compounds C₆₀F₃₈, C₆₀F₄₀, and C₆₀F₄₂ can be obtained. A consecutive change of the main fluorination products (C₆₀F₁₈ and C₆₀F₃₆) takes place at constant temperature (720 K) and on fluorine admission. A quantitative explanation of this fact is given. Selective fluorination of C₆₀(s) by molecular fluorine is compared with solid-phase fluorination using MnF₃(s) as a fluorinating agent.     

Computer modeling of C2 cluster addition to fullerene C60

The reaction between C₂ cluster and C₆₀ fullerene resulting in C₂ insertion to C₆₀ with formation of closed C₆₂ cage (reaction of C₂ ingestion by C₆₀) was investigated by the semiempirical MNDO‐PM3 method. The geometries and energies of extremal points on the C₆₂ potential energy surface were calculated. Several reaction pathways leading to the formation of three different closed C₆₂ fullerenes were investigated. All insertion reactions proceed stepwise through intermediate adducts of different structures. The main reaction pathways were found to be addition of C₂ by its one side to the 6,6‐ or 5,6‐bond of C₆₀ with formation of primary unclosed C₆₂ adducts of “ball‐with‐fork” structures, lying in deep potential wells. Back reaction of C₂ detachment from primary adducts can compete with that of their transformation to the closed C₆₂ cages inasmuch as calculated activation barriers of the both reactions are comparable. Model calculations at the B3LYP/6‐31G* level, using C₃₂H₁₂ semisphere instead of C₆₀, confirmed the conclusion about two competitive pathways of the primary adducts transformation, C₂ detachment, and C₂ ingestion. The concerted insertion of C₂ to C₆₀ was realized only in the case of severe restrictions on starting geometry of the C₂ + C₆₀ system. The results of calculations explain recent experimental data on the formation of metastable adducts upon addition of C₂ to C₆₀, obtained using the time‐of‐flight mass spectrometer with laser desorption. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Preparation and crystal structure of C84(11)Cl20,22, chloro derivatives of a C84 minor isomer

Chlorofullerenes C₈₄(11)Cl₂₀ and C₈₄(11)Cl₂₂ were prepared by chlorination of C₂–C₈₄(11) with VCl₄ at 340–360 °C. An X-ray crystallographic study with the use of synchrotron radiation revealed the chlorination patterns featuring only para additions in C₆Cl₂ hexagons.     

Salt effects on the aggregation behavior of tripolar zwitterionic surfactants with different inter-charge spacers in aqueous solution

Salt effects on the aggregation behavior of tripolar zwitterionic surfactants in aqueous solutions have been investigated using surface tension, dynamic light scattering (DLS), freeze-fracture transmission electron microscopy (FF-TEM), and ¹H NMR. The tripolar zwitterionic surfactants with different inter-charge spacers are [C₁₄H₂₉(CH₃)₂N⁺C_sN⁺(CH₃)₂CH₂CH₂CH₂SO₃ ^?]Br^? (C₁₄C_sTri, C_s?=?–(CH₂)₂–, –(CH₂)₆–, –(CH₂)₁₀–, and p-xylyl). It is found that the critical micelle concentration (CMC) values of the corresponding traditional zwitterionic surfactant C₁₄H₂₉(CH₃)₂N⁺CH₂CH₂CH₂SO₃ ^? (TPS) are almost constant with the increase of the NaBr concentration. However, the CMC values of C₁₄C_sTri decrease sharply at a lower NaBr concentration and then level off at a higher NaBr concentration. Moreover, the decreasing extents of the CMC values for C₁₄C₂Tri, C₁₄C₆Tri, and C₁₄C_pxTri are very close, but more significant than that for C₁₄C₁₀Tri, suggesting that the self-assembly ability of the tripolar zwitterionic surfactants with a longer inter-charge spacer is less sensitive to NaBr. The DLS and FF-TEM results reveal that C₁₄C₂Tri, C₁₄C₆Tri, and C₁₄C_pxTri form micelles without NaBr and that the size slightly increases with the increase of NaBr concentration, whereas micelles and vesicles coexist for C₁₄C₁₀Tri and TPS without NaBr and then transfer to micelles upon the addition of NaBr. The salt-induced morphological transition for C₁₄C₁₀Tri is further studied using ¹H NMR. The addition of NaBr reduces both the electrostatic repulsion between the same charged ammoniums and the electrostatic attraction between the oppositely charged ammonium and sulfonate. Thus, the longer inter-charge spacer of C₁₄C₁₀Tri tends to be more bended and the sulfonate group becomes available to contact the ammonium, which promotes micellization.     

Photodecomposition reaction of ethyl bromide at 147 nm

A vacuum ultraviolet photolysis of C₂H₅Br at 147 nm was studied over a pressure range of 0.5–50 torr at 298 K. The effects of additives He and NO were also investigated. The principal reaction products were found to be C₂H₄ and C₂H₆, with lesser yields of CH₄ and C₂H₂. With increasing pressure the product quantum yields Φ_i of C₂H₄, CH₄, and CH₂H₆ remained constant, while that of C₂H₂ decreased from 0.03 to almost 0. The effect of He as an additive was found to be extremely small on the quantum yields of the major products. Addition of NO completely suppresses the formation of CH₄, C₂H₂, and C₂H₆, and reduces partially the production of C₂H₄. The primary processes appear to involve two electronically excited states. One state mainly yields C₂H₄ by molecular elimination of HBr and is thought to be due to a Rydberg transition. The other state decomposes to C₂H₅ and Br radicals by C? Br bond fission. These two competitive reaction modes contribute to the photodecomposition in proportions of 50% and 50%. The extinction coefficient for C₂H₅Br at 147 nm and at 298 K has been determined as ? = (1/PL) In(I_o/I_t) = 712 ± 7 atm^?1 · cm^?1.     

Direct synthesis using gold atoms: synthesis,infrared and ultraviolet-visible spectra and molecular orbital investigations of monoethylene gold(0), (C2H4Au

The reaction of Au atoms with ¹²C₂H₄ or ¹²C₂H₄/Ar mixtures at 8–10 K yields a single product. Using Au and ¹²C₂H₄ concentration experiments, warm-up studies and ¹³C₂H₄/Ar, ¹²C₂H₄/¹³C₂H₄/Ar isotopic substitution, coupled with infrared and UV-visible spectroscopy, the product is characterized to be monoethylene gold(0), (C₂H₄)Au, the first reported example of a zerovalent gold-olefin complex. Extended Hückel molecular orbital calculations proved to be a useful aid towards the assignment of the optical spectrum of (C₂H₄)Au. The thermal stability of (C₂H₄)Au in solid C₂H₄ at 70 K is discussed in terms of the feasibility of a macroscale, liquid nitrogen temperature, chemical synthesis. The molecular and electronic properties of the group of complexes (C₂H₄)M and M(0₂), where M = Ag or Au, are compared and discussed.