Metal-directed two new Anderson-type polyoxometalate-based metal–organic complexes with different electrocatalytic sensing performance

Two new Anderson-type polyoxometalate (POM)-based metal–organic complexes, namely: H[Cd(L)(CrMo6(OH)6O18)]·2H2O (1) and H[Co(L)(CrMo6(OH)6O18)(H2O)2]·3H2O (2) (L = N, N'-bis(3-pyridinecarboxamide)-1,4 cyclohexane) have been successfully synthesized under hydrothermal condition and characterized in detail. For 1, the [CrMo6(OH)6O18]3- anion adopts hexadentate coordination pattern connecting with binuclear Cd2II unit to form a two-dimensional (2D) layer, which is further expanded into a three-dimensional framework by the L ligands. In 2, The CrMo6 anions exhibit tetradentate coordination mode to connect the metal ions constructing a 2D layer. The L ligand does not play a linkage role and only suspend on the 2D network, which is different from complex 1. The influence of central metal ions on the architectures was discussed. The electrocatalytic reduction of potassium bromate and the electrocatalytic oxidation of ascorbic acid by complexes 1 and 2 were investigated. These title complexes could be regarded as amperometric sensors for the detection of potassium bromate and ascorbic acid. In particular, complex 1 shows the lowest detection limit for these two substances, suggesting its better electrochemical performance.