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

Abstract

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.