Rational Synthesis, Structure, Magnetism and Electrochemistry of Mixed Iron-Nickel-Containing Wells-Dawson-Fragment-Based Sandwich-Type Polyoxometalates.

The compound [Na 2 (H 2 O) 2 Ni 2 (As 2 W 15 O 56 ) 2 ] 18- , Ni2As4, was synthesized and structurally characterized for the first time by X-ray crystallography. This complex reacts with Fe III to form two new mixed-metal sandwich-type complexes, [Fe 2 (H 2 O) 2 Ni 2 (As 2 W 15 O 56 ) 2 ] 14- , Fe2_Ni2As4, and [Fe(H 2 O). Ni(H 2 O)Ni 2 (As 2 W 15 O 56 ) 2 ] 15- , FeNi-Ni2As4. In comparison, the synthesis of the previously reported complex [Na 2 (H 2 O) 2 -Fe 2 (As 2 W 15 O 56 ) 2 ] 16- , Fe2As4, was rationalized and improved, and the incorporation of Ni II into the latter compound leads to the new mixed-metal complex [Ni 2 (H 2 O) 2 Fe 2 (As 2 W 15 -O 56 ) 2 ] 14- , Ni2_Fe2As4. Complete characterization of these complexes by FTIR, UV/Vis, elemental analysis, magnetic measurements and X-ray crystallography, wherever possible, clearly defined their electronic and structural properties. These complexes undergo multiple electron-transfer processes and are effective in the electrocatalytic reduction of nitrite, dioxygen and hydrogen peroxide.