Reduction of sodium permanganate with sodium iodide in aqueous solutions has been investigated systematically. The products formed have been characterized by X-ray di4raction, wet-chemical analysis, and surface area and magnetic susceptibility measurements after 5ring at various temperatures. The results reveal that the sodium content x in the reduction products Na x MnO 2؉ depends strongly on the reaction pH and mildly on the relative concentrations of the reactants. Na 0.7 MnO 2؉ obtained at pH > 11 followed by 5ring at T > 5003C adopts the P2 layer structure (hexagonal) with cation vacancies arising from a +0.3. Na 0.7 MnO 2؉ crystallizing in a distorted P2 structure (orthorhombic) without cation vacancies ( +0) could be obtained by annealing the hexagonal Na 0.7 MnO 2؉ ( +0.3) in N 2 atmosphere around 6003C. While the orthorhombic Na 0.7 MnO 2؉ ( < 0.05) is stable during ion-exchange reactions with lithium salts at 254T41803C, the hexagonal Na 0.7 MnO 2؉ ( +0.3) transforms to spinel-like phases due to the presence of cation vacancies. Na 0.5 MnO 2؉ obtained at a controlled pH of 9.3 adopts a metastable layer structure on 5ring at 5003C and a tunnel structure isostructural with Na 4 Mn 4 Ti 5 O 18 on 5ring at T56003C. The tunnel structure is stable to ion-exchange reactions without transforming to spinel-like phases. In addition, washing the reduction products with various organic solvents before 5ring at higher temperatures is found to in6uence the reaction kinetics, composition, and crystal chemistry.
2001 Academic Press
The reduction of sodium permanganate with sodium iodide was performed by two procedures. In the "rst procedure, 100 mL of 0.5 M aqueous solution of NaMnO ) H O was