Cd(II)-Coordination Framework: Synthesis, Anion-Induced Structural Transformation, Anion-Responsive Luminescence, and Anion Separation

A series of Cd­(II) coordination frameworks that are constructed from a new oxadiazole-bridged ligand 3,5-bis­(3-pyridyl-3-(3′-methyl­phenyl)-1,3,4-oxadiazole (<b>L</b>) and CdX₂ (X = NO₃^–, Cl^–, Br^–, I^–, N₃^–, and SCN^–) were synthesized. The NO₃^– anion of the solid Cd­<b>L</b>₂­(NO₃)₂·2THF (<b>1</b>) is able to be quantitatively exchanged with Cl^–, Br^–, I^–, SCN^–, and N₃^– in the solid state. For Cl^– and Br^–, the anion exchange resulted in a anion-induced structural transformation to form the structures of <b>2</b> and <b>3</b>, respectively. In addition, the Cd­(II) structure herein exhibits the anion-responsive photoluminescence, which could be a useful method to monitor the anion-exchange process. Notably, compound <b>1</b> can recognize and completely separate SCN^–/N₃^– with similar geometry.