Sandwich-Type Phosphotungstates: Structure, Electrochemistry, And Magnetism Of The Trinickel-Substituted Polyoxoanion [Ni3na(H2o)(2)(Pw9o34)2](11-)

The novel nickel-substituted, dimeric phosphotungstate [Ni3Na(H2O)(2)(PW9O34)(2)](11-) (1) has been synthesized and characterized by IR spectroscopy, elemental analysis, and electrochemistry. X-ray single-crystal analysis was carried out on Na-11[Ni3Na(H2O)(2)(PW9O34)(2)].21.25H(2)O, which crystallizes in the triclinic system, space group P (1) over bar, with a = 12.2467(6) Angstrom, b = 16.6031(7) Angstrom, c = 22.4017(12) Angstrom, alpha = 73.9870(10)degrees, beta = 87.6060(10)degrees, gamma = 79.344(2)degrees, and Z = 2. The polyanion consists of two lacunary B-alpha-[PW9O34](9-) Keggin moieties linked via three nickel(II) centers and a sodium ion. The structure of 1 is composed of two fused Keggin fragments that represent different Baker-Figgis isomers (alpha- vs beta-type). Electrochemical studies show that 1 exhibits a stable and reproducible voltammetric pattern, with a first wave featuring a chemically reversible four-electron/four-proton process, An investigation of the magnetic properties indicates that the three nickel centers exhibit ferromagnetic exchange interaction.