Electrocatalytic and Hg Fluorescence Identifiable Bifunctional Sensors for a Series of Keggin Compounds.

By using a 2,2'-dimethyl-4,4'-bithiazole (dm4bt) ligand, Keggin polyanions, and different metal ions, nine Keggin-based compounds, namely, {[Ag(dm4bt)][Ag(dm4bt)]}(PWO)(HPWWO) (1), [Cu(dm4bt)][Cu(dm4bt)(PWO)] (2), [Cu(dm4bt)](SiWO) (3), {[Zn(dm4bt)](SiWO)} (4), [Zn(dm4bt)(HO)](HPMoMoO)·2HO (5), [Zn(dm4bt)(MoO)] (6), [Cd(dm4bt)][Cd(dm4bt)(HO)(PMoO)]·2HO (7), [Cd(dm4bt)](PMoO)·(Hdm4bt) (8), and [Cd(dm4bt)(HO)](HPMoMoO)·2HO (9), have been hydrothermally synthesized and characterized by single-crystal X-ray diffraction analysis, IR spectroscopy, and elemental analyses. Compounds 1-9 are zero-dimensional structures except compound 6, which exhibits a one-dimensional structure. In compound 1, there are three isolated subunits: Keggin anions, binuclear [Ag(dm4bt)], and mononuclear [Ag(dm4bt)] clusters. The binuclear [Ag(dm4bt)] cluster has a Ag-Ag bond. In compound 2, a monosupporting anion {[Cu(dm4bt)](PWO)} and an isolated [Cu(dm4bt)] cluster exist. By changing the transition metal ions, we obtained two different structures: a supramolecular 3 and a bisupporting anion in 4. By a one-pot method, we successfully obtained compounds 5 and 6, 7 and 8, respectively. In compound 5, the [Zn(dm4bt)(HO)] subunit links adjacent PMo anions via S···O interactions to form a one-dimensional (1D) supramolecular chain. In compound 6, some PMo ions have transformed to [MoO] chains. The [Zn(dm4bt)] clusters buckle up and down the chain. Compound 7 has a monosupporting anion and an isolated [Cd(dm4bt)] cluster. Compound 8 has isolated anions and [Cd(dm4bt)] clusters. By changing the pH of 7 and 8, a distinct supramolecular compound 9 was obtained. Additionally, the optical band gap, electrochemical, and photocatalytic properties of 1-9 have been investigated in detail. The carbon paste electrodes can be used as bifunctional amperometric and fluorescence sensors for recognition of Hg. The n-CPEs as electrochemical sensors can show accurate selectivity for NO ions in some common ions. In the fluorescence sensor experiment, fluorescence intensities decrease more than 80% when quenched by Hg.