Luminescent group 12 metal tetracarboxylate networks as probe for metal ions

Abstract

Hydrothermal in situ decomposition of DMF generated three [NH₂(CH₃)₂]⁺ cation templated anionic zinc and cadmium terphenyl-3,2′′,5′′,3′-tetracarboxylate (tpta) frameworks. Compound 1 shows a kgd topological layer constructed by 6-connected paddlewheel-type [Zn₂(CO₂)₄] SUBs and 3-connected tpta groups. Compound 2 has a 3D sra network constructed by the zigzag chains of metal centers and tpta groups. Compound 3 adopts a new (4,7)-connected topological network with four types of nodes. Compounds 1–3 show two blue phosphorescent emission bands attributed to ligand centered transitions perturbed by metal ions, which displays significant temperature-dependent behavior. The higher energy emissions are red-shifted and weakened with increasing temperature, while the lower energy emissions increase in intensity and finally become the main emission bands; the CIE coordinates for 1 are changed with decreasing temperature from blue to greenish blue. Interestingly, 1 could selectively detect traces of Ca²⁺ ions at ppm level in a pyridine suspension, which makes it more suitable to be a luminescent probe for sensing Ca⁺ ions.