Carbazole-based bis-imidazole ligand-involved synthesis of inorganic–organic hybrid polyoxometalates as electrochemical sensors for detecting bromate and efficient catalysts for selective oxidation of thioether

Considering the potential application on preparing electrode and catalyst materials of inorganic-organic hybrid polyoxometalates, a bis-imidazole ligand with carbazole as a connector, 3,6-di(1H-imidazol-1-yl)-9H-carbazole (L), was used for preparing inorganic-organic hybrid polyoxometalates. As a result, three complexes formulated by [NiL2(Mo2O7)] (1), [Cu(H2O)2(HL)2 (β-Mo8O26)]·H2O (2) and [Ni2(H2O)4L2 (CrMo6(OH)5O19)]·6H2O (3) were obtained successfully. Structural analysis indicated that the different polyoxoanions and metal ions showed important influences on the formation of structures. In the presence of Ni2+ ions and heptamolybdate, a 2D network constructed from Ni2+ ions and L ligands was formed in complex 1, in which the [Mo4O14]4- polyoxoanions were encapsulated. But the use of Cu2+ ions led to a 1D chain of complex 2, which was composed of [β-Mo8O26]4- polyoxoanions and mononuclear {CuL2} units. By utilizing [CrMo6(OH)5O19]4- as the inorganic building block, complex 3 showed a 2D (4, 4)-connected layer. Complexes 1-3 could be employed as electrode materials for sensing bromate with the limits of detection of 0.315 μM for 1, 0.098 μM for 2 and 0.551 μM for 3. Moreover, these complexes showed efficient catalytic activity for the selective oxidation of thioethers.