Systematic assembly of {LnMnIII4} appended cubanes with inorganic polyoxometalate ligands and their electrocatalytic property

Exploration of the reactivity of the versatile polyoxometalate precursor [β2-SiW11O39]8 − with lanthanide cations, transition-metal cations, carbonate, and morpholine, afforded a group of new appended cubanes {LnMnIII4} (Ln = HoIII, TmIII, YbIII, SmIII, GdIII, ErIII and CeIV). The appended cubanes {LnMnIII4} were encapsulated by two inorganic polyoxometalate ligands, resulting in a series of heterometallic cluster-based sandwich-type compounds: K10Na3[{LnIIIMnIII4(μ3-O)2(μ2-OH)2(H2O)(CO3)}(β-SiW8O31)2]·xH2O (Ln = HoIII, x = 24 for 1; Ln = TmIII, x = 22 for 2; Ln = YbIII, x = 21 for 3); K7Na6[{LnIIIMnIII4(μ3-O)2(μ2-OH)2(H2O)(CO3)}(β-SiW8O31)2]·xH2O (Ln = SmIII, x = 22 for 4; Ln = GdIII, x = 20 for 5; Ln = ErIII, x = 22 for 6) and K7Na5[{CeIVMnIII4(μ3-O)2(μ2-OH)2(H2O)(CO3)}(β-SiW8O31)2]·24H2O (7), which were characterized by single-crystal X-ray diffraction analyses, IR spectroscopy, and thermal gravimetric analysis. Electrocatalytic study reveals that these compounds exhibited the activity of electrocatalytic reduction of sodium nitrite.