A dimeric polyoxometalate sandwich motif containing a truncated {Mn3O4} cubane core

A novel sandwich-type silicotungstate motif, K18[MnII2{MnII(H2O)5MnIII3(H2O)(B-β-SiW9O34)(B-β-SiW6O26)}2]·20H2O 1, has been isolated from the reaction of K8[γ-SiW10O36]·12H2O and manganese ions in aqueous acidic media. The transition metal-substituted polyoxometalate (TMSP) 1 has been fully characterized by single-crystal X-ray diffraction, elemental analysis, thermogravimetric analysis, and infrared spectroscopy. This dimeric polyanion consists structurally of the sandwich polyanion {MnII(H2O)5MnIII3(H2O)(B-β-SiW9O34)(B-β-SiW6O26)}, dimerized via two manganese(II) linker ions. Each monomeric unit is composed of two non-equivalent Keggin fragments, (B-β-SiW8O31) and (B-β-SiW6O26), linked to each other via three manganese ions resulting in a truncated {Mn3O4} cubane core. Experimental, structural, and electrochemical aspects of the material are reported and discussed.