Cobalt complexes tuned by Anderson-type polyoxometalates and bis-amide derivative ligands featuring a ‘V’-like connector for efficient ampere sensing and the visible-light catalytic reduction of Cr(vi)

To exploit polyoxometalate (POM)-based metal-organic complexes (MOCs) with outstanding electro- and photo-chemical performances, two new bis-amide derivative N-donor ligands featuring a 'V'-like connector, 4,4'-bis(3-pyridinecarboxamide)phenylmethane (L1) and 4,4'-bis(3-pyridinecarboxamide)phenylketone (L2), were designed and reacted with Anderson-type POMs in the presence of Co(II) ions under solvothermal conditions, which generated four MOCs: [Co2(L1)2(AlMo6H5O24)]·4H2O (1), [Co2(HL1)2(H2O)6(TeMo6O24)]·2H2O (2), [Co2(HL2)2(H2O)4[AlMo6H6O24]2]·5H2O (3), and [Co2(HL2)2(H2O)6(TeMo6O24)]·2H2O (4). All the complexes showed supramolecular structures via hydrogen bond interaction, which resulted from the 2D layers for 1, the satellite-like structural units for 2 and 4, but the 1D chains for 3. In these structures, the POMs and organic ligands exhibited different coordination modes. Both 2 and 4 showed efficient ampere sensing activities for Cr(VI) with lower limits of detection of 0.029 and 0.038 μM, respectively. Complexes 1 and 2 showed good visible-light catalytic behavior toward the reduction of Cr(VI), which offers more chances for developing electrochemical sensors and photocatalysts for Cr(VI).