Hydrothermal syntheses and characterization of a series of luminescent Cd(ii) frameworks with pyridine-based and benzene-based bis-triazole ligands

Abstract

Using the pyridine-based and benzene-based bis-triazole ligands 2,6-di-(1,2,4-triazole-4-yl)pyridine (L₁) and 1,4-di-(1,2,4-triazole-4-yl) benzene (L₂), a series of luminescent Cd(II) coordination polymers, namely, [Cd(μ₂-L₁)₂I₂]_n (1), {[Cd₃(μ₃-L₁)₆](BF₄)₅(PF₆)·18H₂O}_n (2), [Cd(μ₂-L₂)I₂]_n (3), [Cd(μ₂-L₂)(μ_1,3-NCS)₂]_n (4), {[Cd(μ₂-L₂)(L₂)(H₂O)₃]SiF₆·3H₂O}_n (5), {[Cd(μ₂-L₂)(L₂)(H₂O)₃]SiF₆·CH₃OH·2.5H₂O}_n (6), {[Cd(μ₂-L₂)₃](BF₄)₂}_n (7) and {[Cd(μ₂-L₂)₃](ClO₄)₂}_n (8), have been isolated. 1 represents a novel 2D framework containing 1D infinite right- and left-handed helical chains. 2 is a 3D coordination framework based on trinuclear Cd(II) clusters containing triangular channels, in which eighteen free water molecules, five free BF₄⁻ and one free PF₆⁻ anions are located. For 3, the L₂ ligands can bridge Cd^II centers forming a 1D chain, while for 4 the L₂ and μ_1,3-NCS⁻ co-ligands can further bridge Cd^II centers forming a 2D corrugated layer. 5 and 6 represent a novel coordination framework containing 1D rhombic nano-porous channels, in which free SiF₆²⁻ anions and free solvent molecules are located. 7 and 8 also represent a novel coordination framework containing another kind of trianglular nano-porous channel, in which free BF₄⁻ or ClO₄⁻ anions are located. Solid-state fluorescent spectra of 1–8 have been determined indicating strong fluorescent emission bands. The result also reveals that L₁ and L₂ can adopt versatile coordination modes and have great potential in the construction of these highly-dimensional luminescent coordination frameworks.