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

The reaction of Zn(OAc)2·2H2O, NH4F, and 2,6-dimethylbenzo[1,2-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)8]8+ building blocks interconnected via coplanar [Zn4F2(Rim)2]4+ 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)8]8+ 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.