Lacunary Wells-Dawson sandwich complexes - Synthesis, characterization, and stability studies of multi-iron species

Reaction of alpha-Na-12(As2W15O56) with Fe-II in 1 M NaCl solution followed by air oxidation yields alphaalphaalphaalpha-H2Na14[(NaOH2)(2)Fe-2(III)(As2W15O56)(2)] (Na2), the arsenic analogue of the divacant lacunary sandwich, alphaalphaalphaalpha-H2Na14[(NaOH2)(2)Fe-2(III)(P2W15O56)(2)] (Na1). This complex (Na2) consists of a Na2Fe2 central unit sandwiched between two B-alpha-As2W15O5612- moieties. Both Na1 and Na2 react with one equivalent of Fe-III to give alphaalphabetaalpha-Na-14[(NaOH2)((FeOH2)-O-III)(Fe-III)(2)(X2W15O56)(2)], where X = P (Na3) or As (Na4), or two equivalents of Mn-II to give alphabetabetaalpha-Na-14[((MnOH2)-O-II)(2)(Fe-III)(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) Angstrom, b = 13.9327(9) Angstrom, c = 21.3347(13) Angstrom, alpha = 92.921(l) degrees, beta = 94.367(1) degrees, gamma = 118.154(1) degrees, triclinic, P (1) over bar, R1 = 5.49%, based on 24662 independent reflections], which revealed a Mn2Fe2 central unit sandwiched between two B-alpha-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. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).