Three keggin-templated compounds constructed by flexible ligands: syntheses and electrochemical properties

By using the Keggin anion [SiMo12O40](4-) as a template and bis(triazole) derivatives as organic ligands, three compounds were synthesized, [Zn-2(bte)(4)(SiMo12O40)]center dot H2O (1), [Zn-4(btb)(8)(SiMo12O40)(2)] (2) and [Zn-2(bth)(4)(SiMo12O40)] (3) (bte = 1,2-bis(1,2,4-triazol-1-yl)ethane, btb = 1,2-bis(1,2,4-triazol-1-yl)butane and bth = 1,2-bis(1,2,4-triazol-1-yl)hexane). Compound 1 has a cross-shaped cycle-connecting-cycle chain, with two Keggin anions locating above and below for each cycle. By increasing the spacer length of the ligands, a 2D double-layer is formed in 2. The Keggin anions are embedded in the grids of the double-layer. Compound 3 exhibits a wave-like 2D layer with large grids. The two layers penetrate in the form of crests to crests. The anions are covered by these two penetrated layers. The Keggin anions induce distinct metal-organic subunits in 1-3 as the templates. We found that these compounds show electrocatalytic activity for ascorbic acid, bromate and nitrite. All these compounds can be used as electrochemical sensors for nitrite and show good selectivity for NO2- ions.