Lacunary Wells−Dawson Sandwich Complexes − Synthesis, Characterization, and Stability Studies of Multi‐Iron Species

Reaction of α‐Na12(As2W15O56) with FeII in 1 M NaCl solution followed by air oxidation yields αααα‐H2Na14[(NaOH2)2FeIII2(As2W15O56)2] (Na2), the arsenic analogue of the divacant lacunary sandwich, αααα‐H2Na14[(NaOH2)2FeIII2(P2W15O56)2] (Na1). This complex (Na2) consists of a Na2Fe2 central unit sandwiched between two B‐α‐As2W15O5612− moieties. Both Na1 and Na2 react with one equivalent of FeIII to give ααβα‐Na14[(NaOH2)(FeIIIOH2)(FeIII)2(X2W15O56)2], where X = P (Na3) or As (Na4), or two equivalents of MnII to give αββα‐Na14[(MnIIOH2)2(FeIII)2(X2W15O56)2], where X = P (Na5) or As (Na6). A single‐crystal X‐ray diffraction analysis of Na5 has been carried out [a = 13.5387(8) Å, b = 13.9327(9) Å, c = 21.3347(13) Å, α = 92.921(1) °, β = 94.367(1) °, γ = 118.154(1) °, triclinic, P1 , R1 = 5.49%, based on 24662 independent reflections], which revealed a Mn2Fe2 central unit sandwiched between two B‐α‐P2W15O5612− units. All of the new complexes have been characterized by FTIR spectroscopy, UV/Visible spectroscopy, elemental analyses, and cyclic voltammetry, and they are all stable for at least 24 h over a wide pH range (0−7), except for Na4, which is unstable below pH 2. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)