Rational Design of Noncovalent Diamondoid Microporous Materials for Low-Energy Separation of C₆-Hydrocarbons

Abstract

Selective separation of gases/vapors with similar physicochemical properties involves energetically costly distillation processes. Alternative separation processes based on shape-selective molecular sieving, taking place on porous frameworks (or membranes), are less energy demanding but require an optimal balance between selectivity and diffusion kinetics (permeability). Herein, we report a rational strategy to select an optimal soft noncovalent microporous material (NPM) suitable for the low-energy separation of C 6 -hydrocarbons with kinetic diameters in the range of 4.3−6.3 Å. This strategy is based on a Cambridge Structural Database search of diamondoid NPMs with a low packing factor, leading to the selection of an oxidotetrazinc cluster based diamondoid NPM network named DiaMM-1 containing tetrahedral voids of 336 Å 3 (tetrahedron insphere diameter of 5.8 Å accessible through 8.2 Å triangular windows) suitable for this separation. Based on this result the fluorinated analogue DiaMM-2 was designed and synthesized. DiaMM-1 and DiaMM-2 exhibit permanent porosity and high thermal stability. The optimal combination of molecular crystal softness, pore size, and decoration of pore surface of DiaMM-1,-2 leads to high adsorbate diffusivity and low adsorption energy, allowing fast separation of hexane isomers and benzene/cyclohexane mixtures at low temperature.

Tetrahedral M4(μ4-O) Motifs Beyond Zn: Efficient One-Pot Synthesis of Oxido–Amidate Clusters via a Transmetalation/Hydrolysis Approach

“… 3 , 5 , 6 , 16 , 18 , 19 , 21 , 41 − 44 In the hydrolytic transformation, the high Brønsted basicity of alkylzinc moieties is not only used to generate O 2– ions but also facilitates initial deprotonation of the proligand. This approach enabled the synthesis of μ 4 -oxido complexes incorporating a wide range of organic ligands, namely, carboxylates, 5 , 16 , 21 phosphinates, 18 , 19 , 42 amidates, 23 amidinates, 6 , 26 , 41 , 43 and guanidinates. 44 Despite the wide scope of applied [Zn 4 (μ 4 -O)] 6+ core coating ligands, this relatively universal approach for Zn–oxido complexes is essentially non-transferable to the related transition-metal systems.…”

Selective adsorptive separation of cyclohexane over benzene using thienothiophene cages

“…4,[11][12][13] Recently, adsorptive separation employing porous materials has attracted much attention due to the moderate energy demands, dependable recyclability and straight-forward synthetic techniques. [14][15][16][17][18][19][20] Among these porous materials, metal-organic frameworks (MOFs) have been experimentally investigated for the preferential uptake of Bz over Cy. [21][22][23][24] Earlier this year, Sue's and Huang's groups independently achieved the separation of Bz from Cy using nonporous adaptive crystals (NACs) based on pillararene macrocycles.…”

Stepwise Stress‐Induced Transformations of Metal‐Organic Polyhedral Cluster‐Based Assemblies: Where Conformational and Supramolecular Features Meet

“…Polyhedral metal‐oxo clusters [29] have been widely recognized as directional and rigid building units of MOFs [30,31] and functional molecular crystals, [32,33] and can act as gas absorption [34] or small molecules activation sites [35,36] . Thus, an in‐depth understanding of both the primary (PCS) and secondary coordination sphere (SCS) dynamics of building units, as well as supramolecular assemblies is continually vital for the development of supramolecular functional materials [37,38] .…”