Coordinated anion exchange induced structural transformation from a trinuclear cage to a 3D interpenetrated framework with the solvent-mediated mechanism

Reaction of methylene-bis(1,1′-benzimidazole) (mbbz) with CdI2 produces a complex [Cd(mbbz)I2]3 (1) containing the soft coordinated I− anions, which shows a trinuclear cage-like structure. Immersing complex 1 into the aqueous solution of NaN3, we obtained the exchanged product [Cd(mbbz)2(N3)2]n (2). The single-crystal X-ray diffraction shows that complex 2 presents a 3D 2-fold interpenetrating 4-connected framework with 66-dia topology. The results indicate that the soft coordinated I− anions can be completely exchanged by borderline N3− anions, simultaneously, accompanying the structural transformation from a trinuclear cage to a 3D framework. Furthermore, the AFM and EDS data reveal that the exchange is a recrystallization process with solvent-mediated mechanism.

Graphical abstractThe soft coordinated I− anions in [Cd(mbbz)I2]3 (1) were exchanged by borderline N3− anions to give the exchanged product [Cd(mbbz)2(N3)2]n (2). The single crystal structural analysis of the two complexes shows the structural transformation from a trinuclear cage to a 3D 2-fold interpenetrated framework has occurred. Based on AFM and EDS data we confirm that strong coordination anions can be replaced by weak ones, and the exchange is a recrystallization process with solvent mediated mechanism.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The precursor [Cd(mbbz)I2]3 containing soft coordinated I− anions was synthesized. ► The precursor can transform into product [Cd(mbbz)2(N3)2]n via anion exchange. ► The structural transformation is from a trinuclear cage to a 3D framework. ► The soft coordinated I− anions can be exchanged by N3− anions. ► The exchange is a recrystallization process with solvent mediated mechanism.