Multi-iron tungstodiarsenates. Synthesis, characterization, and electrocatalytic studies of alphabetabetaalpha-(Fe(III)OH(2))(2)Fe(III)(2)(As(2)W(15)O(56))(2)(12)(-).
Reaction of the trivacant lacunary complex, alpha-Na(12)[As(2)W(15)O(56)], with an aqueous solution of Fe(NO(3))(3).9H(2)O yields the sandwich-type polyoxometalate, alphabetabetaalpha-Na(12)(Fe(III)OH(2))(2)Fe(III)(2)(As(2)W(15)O(56))(2) (Na1). The structure of this complex, determined by single-crystal X-ray crystallography (a = 13.434(1) A, b = 13.763(1) A, c = 22.999(2) A, alpha = 90.246(2) degrees, beta = 102.887(2) degrees, gamma = 116.972(1) degrees, triclinic, Ponemacr;, R1 = 5.5%, based on 25342 independent reflections), consists of an Fe(III)(4) unit sandwiched between two trivacant alpha-As(2)W(15)O(56)(12)(-) moieties. UV-vis, infrared, cyclic voltammetry, and elemental analysis data are all consistent with the structure determined from X-ray analysis. Magnetization studies confirm that the four Fe(III) centers are antiferromagnetically coupled. A cyclic voltammogram of Na1 reveals that a three-wave W(VI) system replaces the two-wave W(VI) system found in the precursor alpha-As(2)W(15)O(56)(12)(-) complex. The observed modifications in the CV patterns of Na1 and alpha-As(2)W(15)O(56)(12)(-) are most likely due to subsequent changes in the acid-base properties of two reduced POMs that occur as a result of Fe(III) incorporation. Na1 is shown to be more efficient than the monosubstituted complex alpha(2)-As(2)(Fe(III)OH(2))W(17)O(61)(7)(-) in the electrocatalytic reduction of dioxygen. This is attributed to cooperativity effects among the adjacent Fe(III) centers in Na1.
Mbomekalle
Israel Martyr
IM
Laboratoire de Chimie Physique, UMR 8000, CNRS, Université Paris-Sud, Bâtiment 420, 91405 Orsay Cedex, France.
Keita
Bineta
B
Nadjo
Louis
L
Berthet
Patrick
P
Hardcastle
Kenneth I
KI
Hill
Craig L
CL
Anderson
Travis M
TM