Synthesis of a series of 4-pyridyl-1,2,4-triazole-containing cadmium(ii) luminescent complexes

Abstract

Using two 4-substitued triazole ligands, 4-(pyrid-2-yl)-1,2,4-triazole (L₁) and 4-(pyrid-3-yl)-1,2,4-triazole (L₂), a series of novel triazole–cadmium(II) complexes varying from zero- to three-dimensional have been prepared and their crystal structures determined via single-crystal X-ray diffraction. [Cd₂(μ₂-L₁)₃(L₁)₂(NO₃)(μ₂-NO₃)(H₂O)₂](NO₃)₂·1.75H₂O (1) is a binuclear complex containing bidendate, monodedate and free nitrate anions. When the bridging anions SCN⁻ and dca (dca = N(CN)₂⁻) were added to the reaction system of 1, one-dimensional (1D) [Cd(L₁)₂(NCS)₂]_n (2) and two-dimensional (2D) [Cd(L₁)₂(dca)₂]_n (3) were isolated, respectively. When L₂ instead of L₁ was used, [Cd(L₂)₂(NCS)₂(H₂O)₂] (4) and 1D [Cd(L₂)₂(dca)₂]_n (5) were obtained. When the ratio of Cd to L₂ was changed from 1 : 2 to 1 : 1 in the reaction system of 5, three-dimensional (3D) {[Cd₃(μ₂-L₂)₃(dca)₆]·0.75H₂O}_n (6) with 1D microporous channels along the a direction was isolated. Further investigations on other Cd(II) salts and the L₂ ligand in a Cd to L₂ ratio of 1 : 1, an unexpected complex [Cd(μ₂-L₂)(μ₃-SO₄)(H₂O)]_n (7) with a 3D open framework was obtained. All of the complexes exhibit strong blue fluorescence emission bands in the solid state at ambient temperature, of which the excitation and emission maxima are red-shifted to longer wavelength as compared to those in water. Powder X-ray diffraction and thermal studies were used to investigate the bulk nature of the 3D coordination polymers 6 and 7.