Xylene Recognition in Flexible Porous Coordination Polymer by Guest-Dependent Structural Transition

Highly Efficient Separation of Intermediate-Size m-Xylene from Xylenes via a Length-Matched Metal-Organic Framework with Optimal Oxygen Sites Distribution

Xylene separation is crucial but challenging, especially for the preferential separation of the intermediate-size m-xylene from xylene mixtures. Herein, exploiting the differences in molecular length and alkyl distribution among xylenes, we present a length-matched metal-organic framework, formulated as Al(OH)[O2C-C4H2O-CO2], featuring an effective pore size corresponding to m-xylene molecular length combined with multiple negative O hydrogen bond donors distribution, can serve as a molecular trap for efficient preferential separation of the intermediate-size m-xylene. Benchmark separation performance was achieved for separating m-xylene from a ternary mixture of m-xylene/o-xylene/p-xylene, with simultaneous record-high m-xylene uptake (1.3 mmol g-1) and m-xylene/p-xylene selectivity (5.3) in the liquid-phase competitive adsorption. Both vapor- and liquid-phase fixed-bed tests confirmed its practical separation capability with benchmark dynamic m-xylene/p-xylene and m-xylene/o-xylene selectivities, as well as excellent regenerability. The selective and strong m-xylene binding affinity among xylene molecules was further elucidated by simulations, validating the effectiveness of such a pore environment for the separation of intermediate-size molecules.

Gate-opening Induced by C8 Aromatics in a Double Diamondoid Coordination Network

Coordination networks (CNs) that undergo guest-induced structural transformations are of topical interest thanks to their potential utility in separations and storage applications. Herein, we report a double diamondoid (ddi) topology CN, [Ni2(bimpz)2(bdc)2(H2O)] n or X-ddi-2-Ni (H2bdc = 1,4-benzenedicarboxylic acid, bimpz = 3,6-bis(imidazol-1-yl)pyridazine), that undergoes structural transformations induced by C8 isomers, i.e., xylenes (o-xylene, OX; m-xylene, MX; p-xylene, PX) and ethylbenzene (EB). X-ddi-2-Ni was characterized by single-crystal to single-crystal transformations from a nonporous phase, X-ddi-2-Ni-β, to isostructural C8-loaded phases, namely X-ddi-2-Ni-OX, X-ddi-2-Ni-MX, X-ddi-2-Ni-PX and X-ddi-2-Ni-EB. X-ddi-2-Ni accommodates two C8 isomers per Ni unit, resulting in relatively high uptake (ca. 50 wt %), but with low selectivity toward C8 isomers as found using nuclear magnetic resonance (NMR) and gas chromatography (GC). In addition, a narrow range of gate-opening pressures for each isomer was determined from dynamic vapor sorption, consistent with the nonadaptable nature of the C8-loaded phase determined crystallographically, also supported by modeling.

Fine Tuning the Hydrophobicity of a New Three-Dimensional Cu2+ MOF through Single Crystal Coordinating Ligand Exchange Transformations

The synthesis, characterization, and single-crystal-to-single-crystal (SCSC) exchange reactions of a new 3D Cu2+ MOF based on 5-aminoisophthalic acid (H2AIP), [Cu6(μ3-ΟΗ)3(ΑΙΡ)4(HΑΙΡ)]n·6nDMF·nH2O - UCY-16·6nDMF·nH2O, are reported. It exhibits a 3D structure based on two [Cu4(μ3-OH)2]6+ butterfly-like secondary building units, differing in their peripheral ligation, bridged through HAIP-/AIP2- ligands. This compound displays the capability to exchange the coordinating ligand(s) and/or guest solvent molecules through SCSC reactions. Interestingly, heterogeneous reactions of single crystals of UCY-16·6nDMF·nH2O with primary alcohols resulted not only in the removal of the lattice DMF molecules but also in an unprecedented structural alteration that involved the complete or partial replacement of the monoatomic bridging μ3-OH- anion(s) of the [Cu4(μ3-OH)2]6+ butterfly structural core by various alkoxy groups. Similar crystal-to-crystal exchange reactions of UCY-16·6nDMF·nH2O with long-chain aliphatic alcohols (CxH2x+1OH, x = 8-10, 12, 14, and 16) led to analogues containing fatty alcohols. Notably, the exchanged products with the bulkier alcohols UCY-16/n-CxH2x+1OH·S' (x = 6-10, 12, 14, and 16) do not mix with H2O being quite stable in this solvent, in contrast to the pristine MOF, and exhibit a hydrophobic/superhydrophobic surface as confirmed from the investigation of their water contact angles and capability to remove hydrophobic pollutants from aqueous media.

Potential of nonporous adaptive crystals for hydrocarbon separation

Hydrocarbon separation is an important process in the field of petrochemical industry, which provides a variety of raw materials for industrial production and a strong support for the development of national economy. However, traditional separation processes involve huge energy consumption. Adsorptive separation based on nonporous adaptive crystal (NAC) materials is considered as an attractive green alternative to traditional energy-intensive separation technologies due to its advantages of low energy consumption, high chemical and thermal stability, excellent selective adsorption and separation performance, and outstanding recyclability. Considering the exceptional potential of NAC materials for hydrocarbon separation, this review comprehensively summarizes recent advances in various supramolecular host-based NACs. Moreover, the current challenges and future directions are illustrated in detail. It is expected that this review will provide useful and timely references for researchers in this area. Based on a large number of state-of-the-art studies, the review will definitely advance the development of NAC materials for hydrocarbon separation and stimulate more interesting studies in related fields.

Chiral Assembly and Recognition of Seven Copper (II) Coordination Polymers from Tartaric Acid Derivative Ligands

A pair of enantiomeric ligands, (2R,3R)-dibenzyl-2,3-bis(isonicotinoyloxy)succinate ((R,R)-L) and (2S,3S)-dibenzyl-2,3-bis(isonicotinoyloxy)succinate ((S,S)-L), are designed and synthesized. Seven copper (II) coordination polymers {[Cu((R,R)-L)Br 2 (THF)]·CH 3 CN} n ( 1a ) and {[Cu((S,S)-L)Br 2 (THF)]·CH 3 CN} n ( 1b ), {[Cu((R,R)-L)Cl 2 (THF)]·CH 3 CN} n ( 2a ) and {[Cu((S,S)-L)Cl 2 (THF)]·CH 3 CN} n ( 2b ), {[Cu((R,R)-L)(NO 3 ) 2 (CH 3 CN)]} n ( 3a ) and {[Cu((S,S)-L)(NO 3 ) 2 (CH 3 CN)]} n ( 3b ), {[Cu((R,R)-L) 2 (CH 3 CN) 2 ](ClO 4 ) 2 ·3CH 3 CN} n ( 4 ) were obtained through the assemblies with CuBr 2 , CuCl 2 ·2H 2 O, Cu(NO 3 ) 2 ·3H 2 O, Cu(ClO 4 ) 2 ·6H 2 O, respectively. Single-crystal X-ray diffraction and circular dichroism analysis demonstrate that 1a-3a , 1b-3b have a mono chiral one-dimensional (1D) chain-like spiral structure, while 4 have 1D chain-like structure whose metal centers have chiral propeller coordination environment. Ligand structure, anions and solvent systems have a regulatory effect on the formation of chiral helical structure. Further investigation has proved that 1a can be used as circular dichroism spectrum probe for monitoring L-/D-cysteine and L-/D-penicillamine configuration and concentration in aqueous media based on ligand interchange mechanism.

Interpenetrated metal-organic frameworks with enhanced photoluminescence for selective recognition of m-xylene from xylene isomers

Two novel luminescent metal-organic frameworks (MOFs), [Zn₃(TCA)₂(BPB)₂]_n (DZU-101, where H₃TCA = 4,4',4''-tricarboxyltriphenylamine and BPB = 1,4-bis(pyrid-4-yl)benzene) and [Zn₃(TCA)₂(BPB)DMA]_n (DZU-102), based on the same ligands and metal ions were synthesized by regulating the amount of water in the solvothermal reaction system. Structural analyses show that the two MOFs have pillar-layered frameworks with Zn₃ clusters connected by the TCA^3- and BPB ligands. Interestingly, DZU-102 possessed a two-fold interpenetrated framework distinct from the individual network of DZU-101. As a result, DZU-102 showed a visual fluorescence color change from chartreuse to azure in m-xylene, while the fluorescence color was turquoise in p-/o-xylene with no change. Furthermore, compared with p/o-xylene, the fluorescence emission peak of DZU-102 in m-xylene suspension produced an obvious blue shift. Moreover, selective fluorescence sensing experiments were also carried out, which demonstrated that the degree of peak shift was related to the concentration of m-xylene, indicating the potential application of DZU-102 in fluorescence sensing of m-xylene from xylene isomers and further revealed the application of structural interpenetration for luminescence tuning of MOFs.

Chromogenic detection of xylene isomers and luminogenic chemosensing of o-xylene employing a new macrocyclic cobalt complex: synthesis, and X-ray crystallographic, spectroscopic and computational studies

A new binuclear Co(ii) complex, coordinating via two pyridine side-arms linked to two dinaphtho-diazacrown ether macrocyclic ligands, was synthesized and used as a colourimetric and fluorogenic sensor as well as an oxidation catalyst of xylene isomers at room temperature.