What question did this study set out to answer?

This research aims to explore the properties and structural transformations of a new metal azolate framework and its application in selective adsorption.

May 29, 2026

A Highly Stable Metal Azolate Framework Showing Single-Crystal-to-Single-Crystal Structural Transformation and Adsorptive Separation of Toluene/Methylcyclohexane

Key Points

This research aims to explore the properties and structural transformations of a new metal azolate framework and its application in selective adsorption.
Synthesis of metal azolate framework from Zn(OAc)2·2H2O, NH4F, and H2bdmim in isopropanol/ethylene glycol.
Single-crystal X-ray diffraction used to analyze structural transformations upon activation.
Evaluation of thermal and acid-base stability across a range of pH values.
The framework exhibited exceptional thermal stability up to 600 °C and acid-base stability from pH 2 to 13.
Significant framework contraction observed during single-crystal-to-single-crystal transformation, leading to altered coordination modes.
The framework exhibited high selectivity for toluene/methylcyclohexane with a selectivity factor of 52 due to compressed pore channels.

Abstract

The reaction of Zn(OAc)2·2H2O, NH4F, and 2,6-dimethylbenzo1,2-d:4,5-d′diimidazole (H2bdmim) in isopropanol/ethylene glycol yields a new metal azolate framework, Zn2F(OH)(bdmim)(H2O)·Guest (1·G). Single-crystal X-ray diffraction reveals that 1·G comprises irregular decahedral Zn16F8(bdmim)88+ building blocks interconnected via coplanar Zn4F2(Rim)24+ four-membered rings, forming a three-dimensional (3D) framework with diamond (dia) topology featuring cross-linked 1D channels running along the a- and b-axes. Upon activation, 1·G underwent significant framework contraction via single-crystal-to-single-crystal transformation to afford Zn2F(OH)(bdmim) (1a). Interestingly, removal of the aqua ligands prompts the transformation of the monodentate hydroxy ligands into bridging ones to occupy the vacant coordination sites. This structural reconstruction drives elongation of Zn16F8(bdmim)88+ building blocks and simultaneously shortens their interconnection distances, thereby compressing the 1D channels. Moreover, the structure exhibits exceptional thermal stability (up to 600 °C) and robust acid–base stability (pH = 2–13). Additionally, 1a demonstrates high toluene/methylcyclohexane selectivity of 52, which is primarily attributed to their kinetic differences arising from the compressed pore channels.

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