Synthesis, structure and characterization of a new cobalt-containing germanotungstate with open Wells-Dawson structure: K13[{Co(H2O)}(μ-H2O)2K(Ge2W18O66)]

A new germanotungstate K13[{Co(H2O)}(μ-H2O)2K(Ge2W18O66)]·29H2O (1) having an open structure related to the Wells-Dawson anion was firstly synthesized by reacting K8Na2[A-α-GeW9O34] with equivalent of H+ and half equivalent of transition-metal cations in aqueous medium using simple, one-pot procedure, and characterized by means of elemental analyses, TG, FT-IR, UV spectroscopy and X-ray single-crystal analysis. The analysis result indicates the polyoxoanion [{Co(H2O)}(μ-H2O)2K(Ge2W18O66)]13− (1a) drives from the Wells-Dawson structure by breaking four of six W–O–W junctions. One potassium cation that stabilizes the structure is included in the pocket with one Co(II) cation. The investigation of electronic spectrum of the complex in aqueous indicates that the polyoxoanion with open Wells-Dawson structure can transform to Keggin or trivacant Keggin fragment depending on the pH value of the solution. The cyclic voltammetry properties were also studied with the aim of finding out distinctive features.