Effect of three aromatic polycarboxylates on the structural diversities and properties of three new cadmium(II) coordination compounds

Three new cadmium(II) coordination compounds $\left[{\text{Cd}}_2\right(\text{L}{)}_2\left(\text{btec}\right)\left({\text{H}}_2\text{O}{)}_2\right]\cdot {\text{3H}}_2\text{O}$ (1), [Cd(HL)(btb)] (2) and $\left[\text{Cd}\right(\text{L}\left)\right(\text{pda}\left)\right]\cdot {\text{2H}}_2\text{O}$ (3) were prepared by hydrothermal reactions of cadmium(II) chloride with ligands L ($\text{L}=\text{N}$,${\text{N}}^{\prime }$-bis(3-pyridyl)octandiamide) in the presence of different aromatic polycarboxylates (${\text{H}}_4\text{btec}=\text{1,2,4,5-benzenetetracarboxylic acid}$, ${\text{H}}_3\text{btb}=\text{1,3,5-tri(4-carboxylphenyl)benzene}$, ${\text{H}}_2\text{pda}=\text{1,4-phenylenediacetic acid}$). The structures of compounds 1–3 have been determined by X-ray single crystal diffraction analyses and further characterized by infrared spectroscopy (IR), powder X-ray diffraction (PXRD) and thermogravimetric (TG) analyses. Compound 1 displays a 3D metal-organic framework with (4,4,4)-connected $\left\{6^2{.8}^4\right\}\left\{6^3{.8}^3\right\}\left\{6^4{.8}^2\right\}$ topology constructed from 2D $\left[{\text{Cd}}_2\right(\text{btec}){]}_n$ layers and ${\mu }_2$-bridging L ligands. Compound 2 is a 3D (3,3)-connected $\left\{{10}^3\right\}$ topological network based on the 3D $[\text{Cd(btb)}{]}_n^{n-}$ framework and the protonated monodentate HL ligand. Compound 3 shows a 2D layer with (3,5)-connected $(4^2\cdot 6^7\cdot 8)(4^2\cdot 6)$ topological structure, which are further linked by hydrogen bonding interactions to form a 3D supramolecular network. The influences of three aromatic polycarboxylates on the structures of title compounds are investigated. Further, the fluorescent properties of three cadmium(II) compounds and their fluorescent sensing properties towards small solvent molecules and metal cations have been studied.

Graphical Abstract

Three new Cd(II) coordination compounds based on the flexible bis(pyridyl)-bis(amide) ligand and three different polycarboxylates have been hydrothermally synthesized. The polycarboxylates with diverse carboxyl groups and various structures play an important role in constructing three Cd(II) compounds. The thermal stabilities, fluorescent and fluorescence sensing properties of the three Cd(II) compounds towards small solvent molecules and metal cations have been reported. .