New polyoxometalate-templated supramolecular networks based on transition metal ions and pyridine-N-oxide ligands

Two new complexes, [Cu(bppdo)(Hbppdo)(CH3CN)3][PW12O40]·CH3CN·0.5H2O (1) and [Co(2,2′-bpdo)3]2[PWVWVI11O40]·CH3CN·2H2O (2) (bppdo = 1,3-bis(4-pyridyl)propane-N,N′-dioxide, 2,2′-bpdo = 2,2′-bipyridine-N,N′-dioxide), have been synthesized by layering MHPW12O40 salts (M = Cu2+ for 1 and Co2+ for 2) on the organic bppdo (for 1) or 2,2′-bpdo (for 2) ligands with the mixed media of acetonitrile and water at room temperature. Both complexes were fully characterized by elemental analyses, TG analyses, IR, UV–Vis, cyclic voltammetry and single-crystal X-ray diffraction. Both crystal structures exhibit the new polyoxometalate (POM)-templated supramolecular network arrays. The “host” supramolecular networks with large pores are composed of the [Cu(bppdo)(Hbppdo)(CH3CN)3] ring-connected-ring chains for 1 and the [Co(2,2′-bpdo)3] windstick-type units for 2. The “guest” Keggin-type polyoxoanions are located in the pores and dispersed between two organic layers in both complexes. Electrochemical properties of 1 and 2 were investigated and both compounds show the electrocatalytic activity towards the reduction of nitrite.