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

Reaction of α‐Na 12 (As 2 W 15 O 56 ) with Fe II in 1 M NaCl solution followed by air oxidation yields αααα‐H 2 Na 14 [(NaOH 2 ) 2 Fe III 2 (As 2 W 15 O 56 ) 2 ] (Na 2 ), the arsenic analogue of the divacant lacunary sandwich, αααα‐H 2 Na 14 [(NaOH 2 ) 2 Fe III 2 (P 2 W 15 O 56 ) 2 ] (Na 1 ). This complex (Na 2 ) consists of a Na 2 Fe 2 central unit sandwiched between two B‐α‐As 2 W 15 O 56 12− moieties. Both Na 1 and Na 2 react with one equivalent of Fe III to give ααβα‐Na 14 [(NaOH 2 )(Fe III OH 2 )(Fe III ) 2 (X 2 W 15 O 56 ) 2 ], where X = P (Na 3 ) or As (Na 4 ), or two equivalents of Mn II to give αββα‐Na 14 [(Mn II OH 2 ) 2 (Fe III ) 2 (X 2 W 15 O 56 ) 2 ], where X = P (Na 5 ) or As (Na 6 ). A single‐crystal X‐ray diffraction analysis of Na 5 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, P $\bar 1$ , R 1 = 5.49%, based on 24662 independent reflections], which revealed a Mn 2 Fe 2 central unit sandwiched between two B‐α‐P 2 W 15 O 56 12− 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 Na 4 , which is unstable below pH 2. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)