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 [NiL 2 (Mo 2 O 7 )] (1), [Cu(H 2 O) 2 (HL) 2 (β-Mo 8 O 26 )]·H 2 O (2) and [Ni 2 (H 2 O) 4 L 2 (CrMo 6 (OH) 5 O 19 )]·6H 2 O (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 Ni 2+ ions and heptamolybdate, a 2D network constructed from Ni 2+ ions and L ligands was formed in complex 1, in which the [Mo 4 O 14 ] 4- polyoxoanions were encapsulated. But the use of Cu 2+ ions led to a 1D chain of complex 2, which was composed of [β-Mo 8 O 26 ] 4- polyoxoanions and mononuclear {CuL 2 } units. By utilizing [CrMo 6 (OH) 5 O 19 ] 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.