A series of new polyoxometalate-based metal–organic complexes with different rigid pyridyl-bis(triazole) ligands: assembly, structures and electrochemical properties

摘要

Five new polyoxometalate (POM)-based metal–organic complexes (MOCs) with different rigid pyridyl-bis(triazole) ligands, namely, H{Co _(2) (Hpyttz-I) _(2) (H _(2) O) _(6) [CrMo _(6) (OH) _(6) O _(18) ]}·8H _(2) O ( 1 ), {Co _(2) (H _(2) pyttz-I) _(2) (H _(2) O) _(4) [TeMo _(6) O _(24) ]}[Co(H _(2) O) _(6) ]·3H _(2) O ( 2 ), {Co _(3) (Hpyttz-II) _(2) (H _(2) O) _(6) [γ-Mo _(8) O _(26) ]}·10H _(2) O ( 3 ), {Ni _(3) (Hpyttz-II) _(2) (H _(2) O) _(6) [γ-Mo _(8) O _(26) ]}·10H _(2) O ( 4 ), {Ni _(3) (Hpyttz-III) _(2) (H _(2) O) _(8) [γ-Mo _(8) O _(26) ]}·10H _(2) O ( 5 ) (H _(2) pyttz-I = 3-(pyrid-2-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl, H _(2) pyttz-II = 3-(pyrid-3-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl, H _(2) pyttz -III = 3-(pyrid-4-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl), were successfully synthesized and structurally characterized by single-crystal X-ray diffraction, IR spectra, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). Complex 1 is a two-dimensional (2D) supramolecular network based on the binuclear complex unit: [Co _(2) (Hpyttz-I) _(2) (H _(2) O) _(6) [CrMo _(6) (OH) _(6) O _(18) ]]. Complex 2 is a 1D supramolecular chain derived from the binuclear cobalt complex: {Co _(2) (H _(2) pyttz-I) _(2) (H _(2) O) _(4) [TeMo _(6) O _(24) ]} ~(2?) , the discrete [Co(H _(2) O) _(6) ] ~(2+) units act as counter cations. Complexes 3 and 4 are isostructural with different center metals (M = Co or Ni), the adjacent γ-Mo _(8) O _(26) ~(4?) anions are linked by the M ~(II) ions to form a 1D M-γ-Mo _(8) O _(26) inorganic chain. Then 1D M-γ-Mo _(8) O _(26) inorganic chains are linked together by the 1D metal–organic M-(Hpyttz-II) chains to form a 3D framework. In complex 5 , γ-Mo _(8) O _(26) ~(4?) anions are bridged by the Ni ~(II) ions to give a 1D Ni-γ-Mo _(8) O _(26) inorganic chain, the adjacent 1D Ni-γ-Mo _(8) O _(26) chains are connected through [Ni(Hpyttz-III) _(2) ] units to form a 2D layer. The effect of POM type and coordination site of the ligands on the structures of the title complexes were discussed. The title complexes 1 , 2 and 5 exhibit excellent bifunctional electrocatalytic activities toward the reduction of bromate/hydrogen peroxide and the oxidation of ascorbic acid. In addition, the redox potentials of complexes 1 , 2 and 5 are highly sensitive to pH and may be used as a kind of potential pH sensor.