Spatially Confined π-Complexation within Pore-Space-Partitioned Metal-Organic Frameworks for Enhanced Light Hydrocarbon Separation and Purification.

Ultramicroporous metal-organic frameworks (MOFs) are demonstrated to be advantageous for the separation and purification of light hydrocarbons such as C2H2, C2H4, and CH4. The introduction of transition metal sites with strong π-complexation affinity into MOFs is more effective than other adsorption sites for the selective adsorption of π-electron-rich unsaturated hydrocarbon gases from their mixtures. However, lower coordination numbers make it challenging to produce robust MOFs directly utilizing metal ions with π-coordination activity, such as Cu+, Ag+, and Pd2+. Herein, a series of novel π-complexing MOFs (SNNU-33s) with a pore size of 4.6 Å are precisely constructed by cleverly introducing symmetrically matched C3-type [Cu(pyz)3] (pyz = pyrazine) coordinated fragments into 1D hexagonal channels of MIL-88 prototype frameworks. Benifit from the spatial confinement combined with π-complex-active Cu+ of [Cu(pyz)3], pore-space-partitioned SNNU-33 MOFs all present excellent C2H2/CH4, C2H4/CH4, and CO2/CH4 separation ability. Notably, the optimized SNNU-33b adsorbent demonstrates top-level IAST selectivity values for C2H2/CH4 (597.4) and C2H4/CH4 (69.8), as well as excellent breakthrough performance. Theoretical calculations further reveal that such benchmark light hydrocarbon separation and purification ability is mainly ascribed to the extra-strong binding affinity between Cu+ and π-electron donor molecules via a spatially confined π-complexation process.

Micropore Regulation in Ultrastable [Sc3O]-Organic Frameworks for Acetylene Storage and Purification.

High storage capacity, high separation selectivity, and high structure stability are essential for an idea gas adsorbent. However, it is not easy to achieve all three at the same time, even for the promising metal-organic framework (MOF) adsorbents. We demonstrate herein that robust [Sc3O]-organic frameworks could be regulated by a micropore combination strategy for high-performance acetylene adsorption. Under the same solvent system with formic acid as a modulator, similar tritopic ligands extend [Sc3O(COO)6] trigonal-prismatic clusters to generate SNNU-5-Sc and SNNU-150-Sc adsorbents. Notably, the two Sc-MOFs can keep their architectures over 24 h in water at different pH values (2-12) or at 90 °C. Modulated by the linker symmetry, the final stacking metal-organic polyhedral cages produce open window sizes of about 10 Å for SNNU-5-Sc and 5 Å + 7 Å for SNNU-150-Sc. Due to such micropore combinations, SNNU-5-Sc exhibits a top-level C2H2 uptake of 211.2 cm3 g-1 (1 atm and 273 K) and SNNU-150-Sc shows high C2H2/CH4, C2H2/C2H4, and C2H2/CO2 selectivities of 80.65, 4.03, and 8.19, respectively, under ambient conditions. Dynamic breakthrough curves obtained on a fixed-bed column and grand canonical Monte Carlo (GCMC) simulations further support their prominent acetylene storage and purification performance. High framework stability, storage capacity, and separation selectivity make SNNU-5-Sc and SNNU-150-Sc ideal acetylene adsorbents in practical applications.

Tailoring the Pore Environment of a Robust Ga-MOF by Deformed [Ga3O(COO)6] Cluster for Boosting C2H2 Uptake and Separation.

The construction of superstable metal-organic frameworks (MOFs) for selective gas uptake is urgently demanded but remains a great challenge. Herein, a unique bifunctional deformed [Ga3O(COO)6] inorganic secondary building unit (SBU) generated from the desymmetrical evolution of typical triangular prismatic trinuclear cluster was first introduced, which was extended by an isosceles triangular organic linker to produce a robust Ga-MOF (SNNU-63). Remarkably, SNNU-63 can stabilize in water at 25 °C for 96 h and at 80 °C for more than 24 h, which surpasses nearly all other Ga-MOFs. The combined effects of open metal sites and hydrophobic pore environment provided by deformed [Ga3O] SBUs render SNNU-63 with high C2H2 storage capacity and efficient C2H2 and natural gas purification performance. The ideal adsorbed solution theory calculation, column breakthrough tests, and grand canonical Monte Carlo simulations demonstrate that SNNU-63 is a potential material for addressing the challenge of C2H2/CO2 and C2H2/CH4 mixture separation under ambient conditions.

Systematic Regulation of C2H2/CO2 Separation by 3p-Block Open Metal Sites in a Robust Metal-Organic Framework Platform.

The separation of a mixture of C2H2 and CO2 is a great challenge due to their similar molecular sizes and shapes. Al-based metal-organic frameworks (Al-MOFs) have great promise for gas separation applications due to their light weight, high stability, and low cost. However, the cultivation of suitable Al-MOF single crystals is extremely difficult and has limited their explorations up to now. Since In, Ga, and Al are all 3p-block metal elements, a systematic application of the periodic law to investigate 3p-MOFs will undoubtedly help in the understanding and development of worthy Al-MOF materials. Herein, we report the design of a robust 3p metal-organic framework platform (SNNU-150) and the systematic regulation of C2H2/CO2 separation by open 3p-block metal sites. X-ray single-crystal diffraction analysis reveals that SNNU-150 is a 3,6-connected 3D framework consisting of [M3O(COO)6] trinuclear secondary building units (SBUs) and tritopic nitrilotribenzoate (NTB) linkers. Small {[M3O(COO)6]4(NTB)6} tetrahedral cages and extra-large {[M3O(COO)6]10(NTB)14} polyhedral cages connect with each other to generate a hierarchically porous architecture. These 3p-MOFs present very high water, thermal, and chemical stability, especially for SNNU-150-Al, which can maintain its framework at 85 °C in water for 24 h and in a room-temperature environment for more than 30 days. IAST calculations, breakthrough experiments, and GCMC simulations all show that SNNU-150 MOFs have top-level C2H2/CO2 separation performance and follow the order Al-MOF > Ga-MOF > In-MOF.

[Phylogenetic relationship among some groups of orthopteran based on complete sequences of the mitochondrial COI gene].

Complete sequences of the COI gene were used to reconstruct the phylogenetic relationship among 56 species from Orthoptera. We also analyzed the reliability of Orthoptera phylogenetic relationship using translated amino acid sequences of the COI genes. The COI sequences were divided into three data sets on the basis of different codon positions to calculate the Partitioned Bremer support (PBS), and to test the phylogenetic signal in different codon positions of protein-coding genes. The result supports the monophyly of Caelifera and Ensifera; but the monophyly of Acrididae, Catantopidae, Oedipodidae, Arcypteridae and Gomphoceridae are not supported. The P-distances among families vary from 0.107 to 0.153, which are smaller than those of other families, being consist with the classification that these 5 families should be merged into one family (Acrididae). Chrotogonidae and Pyrgomorphidae belong to the superfamily Pyrgomorphoidea. Pamphagidae should be a family alone consistent with Otte's taxonomic system. According to the PBS values, the 3rd and 1st codon positions contribution more for the Phylogenetic tree branches than the 2nd, and longer sequences contain more informative sites. We further demonstrated that it is feasible for phylogenetic studies at family level to use the genetic distances among COI sequences from different species of Orthopera.