A three-component copper phosphonate complex as a sensor platform for sensitive Cd2+ and Zn2+ ion detection in water via fluorescence enhancement

Abstract

A three-component molecular copper phosphonate [Cu2(H4tpmm)2(Hpybim)2]·H2O (1·H2O), where H6tpmm ​= ​2,4,6-tris(phosphorylmethyl)mesitylene and Hpybim ​= ​2-(2-pyridyl)benzimidazole, showing high thermal stability up to approximately 370 ​°C has been prepared. Complex 1·H2O has a dinuclear structure symmetry-related by a crystallographic inversion center, in which the Cu(II) center suits a highly distorted square pyramidal geometry. Complex 1·H2O shows two extremely weak emission bands in both solid state and H2O suspension phase. However, as Cd2+ and Zn2+ were added into the H2O suspension of 1·H2O, the fluorescence intensity would be remarkably enhanced by 11.1 and 25.2 times, respectively, with a dramatic change in the emission band shape. The fluorescence enhancement sensing of 1·H2O toward Cd2+ and Zn2+ in H2O is highly sensitive with limit of detection (LOD) values of 1.35 and 0.89 ​μM, respectively. Such sensing performances are negligibly interfered by most perturbed metal ions but largely affected by Fe3+, Ni2+, and Co2+. EDX and XPS analyses show the occurrence of weak binding interactions between the Cd2+/Zn2+ ions and the structure of 1·H2O, resulting in fluorescence enhancement. This work demonstrates a highly water stable molecular copper phosphonate behaving as a sensor platform suitable for Cd2+ and Zn2+ ion detection in water via remarkable fluorescence enhancement, providing a new method for metal phosphonate complexes.