Since novel magnetic field effects on electroless reactions were found in a superconducting magnet, magnetoelectrochemistry has turned into a new stage, i.e. "high field magnetoelectrochemistry", where the micro-MHD effect, diamagnetic orientation and magnetic force make important roles in electrochemical processes beside the conventional MHD effect. This paper introduces several recent topics in high magnetic field science and describes two symbolic results in magnetoelectrochemistry, i.e. pattern formation of silver electroless deposition and magnetoelectropolymerization of pyrrole.

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Cyclic voltammetric studies of Keggin- and Dawson-type polyoxometalate complexesare reviewed. The voltammetric behavior depends on the solution conditions including the nature of the solvent, the acidity and so on. Both types of polyoxometalates undergo multistep reversible one-electron reductions in neutral media where no protonation accompanies the reduction process. In acidified media, the one-electron waves are converted into two-electron waves, and the transformation behavior is accounted for in terms of the protonation of the reduced form at the electrode surface. Catalytic effects induced by the reduced form of the polyoxometalates are also summarized.

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Voltammetric and Raman and NR spectroscopic studies on the formation of heteropolyoxometalate anions are discussed. Formation conditions of molybdophosphates were compared with those of molybdoarsenates in aqueous solution. The V(V)-substitution reactions of Keggin-type molybdoarsenates were investigated in aqueous and aqueous-organic solutions, which were compared with those of the corresponding molybdophosphates. Novel heteropolymolybdates containing X₂O₇ and XO₃ oxoanions, such as P₂O₇^4-, PHO₃^2- and so on, were isolated as n-Bu₄N⁺ salts in aqueous-organic solution, and their formation conditions were elucidated. A few complexes of them gave four-electron reduction waves. It is noted that water-miscible organic solvents, such as acetonltrlle and acetone, played important roles on the formation and stabilization of heteropolyoxometalate anions.

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