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 (L-1) and 4,4 '-bis(3-pyridinecarboxamide)phenylketone (L-2), were designed and reacted with Anderson-type POMs in the presence of Co(ii) ions under solvothermal conditions, which generated four MOCs: [Co-2(L-1)(2)(AlMo6H5O24)]center dot 4H(2)O (1), [Co-2(HL1)(2)(H2O)(6)(TeMo6O24)]center dot 2H(2)O (2), [Co-2(HL2)(2)(H2O)(4)[AlMo6H6O24](2)]center dot 5H(2)O (3), and [Co-2(HL2)(2)(H2O)(6)(TeMo6O24)]center dot 2H(2)O (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 mu M, 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).