Two three-dimensional cadmium(II) coordination polymers based on 5-amino-tetrazolate and 1,2,4,5-benzenetetracarboxylate: the pH value controlled syntheses, crystal structures and luminescent properties

By a pH value controlled synthesis strategy, hydrothermal reactions of Cd(NO3)2·4H2O with mixed-ligands of 5-amino-tetrazole (Hatz) and 1,2,4,5-benzenetetracarboxylic acid (H4btec) yielded two 3D cadmium(II) coordination polymers (CPs) of {K[Cd2(atz)(btec)(H2O)2]}n (1) and [Cd3(OH)(atz)(btec)(H2O)2]n·nH2O (2). Their structures were determined by elemental analysis (EA), infrared spectra (IR), thermogravimetric analysis (TGA) and single-crystal/powder X-ray diffraction. The results reveal that both 1 and 2 are 3D architectures. In 1, the Cd(II) ions are connected together by μ2-atz and μ6-btec4−, generating a rare (4,6)-connected anion framework. The anti-cation K+ ions locate the micropores and weakly interact with the carboxyl oxygen of the μ6-btec4− ligands. In 2, six Cd(II) ions are linked together through two μ3-OH− and two μ3-atz− to form a [Cd6(μ3-OH)2(μ3-atz)2]8+ unit, which is further connected with other equivalent units by μ9-btec4− spacers, resulting in a rare (5,10)-connected porous framework. The photoluminescent investigation illustrates that 1 and 2 show strong emissions at 470 and 457 nm upon excitation at 350 and 370 nm, respectively.