REDUCTION OF OXIDES BY SODIUM-BOROHYDRIDE SOLUTIONS - A CHIMIE DOUCE PREPARATION OF OXIDE BRONZES

This work describes the use of sodium borohydride at room temperature as a reducing agent in aqueous medium in order to prepare oxide bronze s in which a cation is inserted. Two possibilities are offered dependi ng on pH: a topotactic reaction leading to a final compound isostructu ral with the starting oxide, or a non-topotactic reaction leading to a bronze which may differ significantly from the parent phase. They are illustrated by two examples, respectively: the preparation of a hexag onal potassium tungsten bronze from a metastable hexagonal WO3 (conser vation of the tunnel structure), and that of the lamellar vanadyl vana date (NH4)(2)V3O8 from the stable form of V2O5. (C) Academie des scien ces/Elsevier, Paris.