The development of advanced materials for selective separation of xylene isomers remains a key challenge in petrochemical processing. This study introduces a new heterometallic metal-organic framework, [Li₂Zn₂(bpy)(ndc)₃] (NIIC-30(Ph)), engineered through the rational use of a preorganized molecular complex to achieve unprecedented selectivity in m-xylene over o-xylene separation. The framework features a three-dimensional network with narrow, tortuous channels lined with aromatic moieties derived from naphthalene-1,4-dicarboxylate and 4,4-bipyridine ligands. These functional groups create a favorable environment for π–π interactions and C–H···π contacts with aromatic guests. Experimental results demonstrate that NIIC-30(Ph) achieves a remarkable m-xylene/o-xylene selectivity of 3.03 in liquid-phase separations, surpassing all previously reported MOFs. The high performance is attributed to both optimal steric fit and enhanced interaction energy: m-xylene fits efficiently within the asymmetric pore without inducing excessive strain, while forming multiple stabilizing contacts. In contrast, o-xylene experiences greater steric hindrance due to its ortho-methyl arrangement, leading to higher framework distortion and reduced binding affinity. Single-crystal X-ray analysis confirms that only one m-xylene molecule per formula unit occupies site B, stabilized by two C–H···π interactions and two CH₃···π contacts, whereas o-xylene exhibits fewer such interactions despite occupying similar positions. The material also shows excellent recyclability, maintaining selectivity after three consecutive separation cycles in both vapor and liquid phases. PXRD and CO₂ sorption measurements confirm structural integrity post-sorption. These findings highlight how precise control over framework topology and functionalization enables superior molecular recognition, establishing NIIC-30(Ph) as a benchmark for industrial xylene separation processes.
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**Enhanced Sorption Performance of Aromatic Molecules in a Preorganized Metal-Organic Framework with Tunable Pore Environment**
This work explores the sorption behavior of aromatic hydrocarbons in a newly synthesized heterometallic MOF, NIIC-30(Ph), whose unique pore architecture enables exceptional selectivity for benzene and specific xylene isomers. The framework’s structure is built from a preorganized [Li₂Zn₂(py)₂(piv)₆] complex, which undergoes controlled substitution to form a rigid, open 3D network with aromatic-rich channels. The resulting system displays type I gas adsorption isotherms for CO₂ and N₂, indicating microporosity, with a BET surface area of 451 m²/g and a pore volume of 0.241 cm³/g. Notably, the material exhibits strong preferential uptake of CO₂ over N₂, with ideal adsorbed solution theory (IAST) selectivity reaching 24.9 at 273 K—highlighting its potential for gas separation applications. For liquid-phase separations, benzene is selectively adsorbed over cyclohexane with a capacity ratio of approximately 4:1, achieving up to 99% benzene enrichment in the adsorbed phase when starting from a 9:1 mixture. This selectivity arises from strong π–π stacking between benzene and the aromatic walls of the channel, which are absent in cyclohexane. In xylene separations, NIIC-30(Ph) demonstrates record-high m-xylene/o-xylene selectivity (3.03), driven by favorable host-guest interactions and minimal framework distortion. The material maintains structural stability across multiple cycles, confirmed by PXRD and gas sorption analyses. The ability to retain functionality after repeated use underscores its practical viability. Overall, this study illustrates how integrating preorganized complexes into MOF synthesis enables the creation of highly selective, stable materials tailored for complex molecular separations.
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**Single-Crystal Structural Analysis Reveals Molecular Recognition Mechanisms in a Functionalized Metal-Organic Framework**
A comprehensive single-crystal X-ray diffraction study of guest-inclusion compounds of NIIC-30(Ph) provides direct evidence of the molecular recognition mechanisms responsible for its high selectivity. Crystals soaked in benzene or xylenes reveal distinct guest locations and interaction patterns within the confined channels. Benzene molecules occupy four independent sites: A (on a 2-fold axis), D (on an inversion center), and B/C (symmetrically disordered). The shortest C···C distances range from 3.51 to 3.81 Å, indicating strong non-covalent interactions with the aromatic ligands.HMGA1 Antibody Autophagy Specific C–H···π and C–H···O contacts stabilize each guest, with some distances shorter than those observed in crystalline benzene, suggesting enhanced binding affinity.203787-91-1 SMILES For xylene isomers, p-xylene and m-xylene bind primarily at site B, where they engage in multiple CH₃···π and C–H···π interactions with ndc²⁻ and bpy ligands.PMID:35161252 In contrast, o-xylene forms fewer stabilizing contacts—only three significant interactions—despite occupying similar positions. Moreover, o-xylene induces the largest channel expansion (4.0 × 9.2 Å), indicating substantial framework deformation. This structural resistance contributes to its lower adsorption preference. The data show that selectivity is not solely based on size but is governed by the number and strength of specific intermolecular interactions. The rigid yet adaptable nature of NIIC-30(Ph) allows it to selectively accommodate preferred guests while excluding others, demonstrating a powerful strategy for molecular recognition in porous materials. These insights pave the way for future design of MOFs with tailored selectivity for complex mixtures of aromatic compounds.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com
