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

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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.

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