Four Keggin-type polyoxometalate-based complexes derived from bis(pyrazine)-bis(amide) ligands for electrochemical sensing of multiple analytes and adsorbing dye molecules

Four new Keggin-type polyoxometalate (POM)-based metal-organic complexes constructed from two flexible bis(pyrazine)-bis(amide) ligands N,N'-bis(2-pyrazinecarboxamide)-1,2-ethane (bpae) and N,N'-bis(5-methyl-2-pyrazinecarboxamide)-1,2-ethane (bmpae), namely, [Cu-2(bpae)(2)(H2O)(2)(PM(O)(VI)9Mo(V)3O(39))]center dot.5.5H(2)O (1), [Cu-2(bpae)(2)(SiMo12O40)]center dot 3H(2)O (2), ([Co-2(bmpae)(2)(H2O)(4)](SiM2O40))center dot 1.5H(2)O (3), and [Cu-2(bmpae)(2)(SiW12O40)]center dot 8H(2)O (4), have been hydrothermally synthesized and structurally characterized. Complex 1 is a [PM(O)(IV)9MO(V)3O(3)9](4-) (PMo12)-based 3D coordination framework, which is constructed by three kinds of 1D chains: [Cu(bpae)](n)(2n+) [PMo12](n)(4n-) and [Cu(PMo12)](n)(2n- )chains. Complex 2 shows a 2D structure, which is composed of tridentate [SiMo12O40](4-) anions (SiMo12) and [Cu(bpae)](n)(2n+) chains. Complex 3 is a 0D structure, which is constructed from [Co-2(bmpae)(2)](4+) binuclear rings and discrete [SiW12O40](4-) (SiW12) anions. In 4, the 1D [Cu(bmpae)](n)(2n+) chains are connected by the SiW12 anions to produce a 2D structure. The diverse structures of 1-4 demonstrate that the different metal ions and POMs have pivotal influences on the formation of the final coordination frameworks. In this work, the adsorption performances of 1-4 for the organic dyes gentian violet (GV) and methylene blue (MB) were examined, and 1 possesses good reusability. In addition, 1-4 can be employed as amperometric sensors to identify multiple analytes (BrO3-, NO2-, Cr(VI) and Fe(III) ions) and possess good selectivity in the presence of some other ions.