CHEMISTRY OF BOROHYDRIDE REDUCTION OF IRON(II) AND IRON(III) IONS IN AQUEOUS AND NONAQUEOUS MEDIA - FORMATION OF NANOSCALE FE, FEB, AND FE2B POWDERS

The reduction of FeBr2(aq), FeBr3(aq), FeBr2(diglyme), and FeBr3(digly me) by NaBH4 has been investigated with mechanistic and stoichiometric factors in mind. The bewildering complexity of such reactions has bee n partly alleviated. We find that the primary products are different d epending on the reaction medium. In aqueous solution Fe2+ yields mainl y noncrystalline, nanoscale Fe(s), while in dry diglyme the product is nanoscale Fe2B. In the case of Fe3+(aq) the primary product again is Fe(s), but in diglyme it is FeB. An unexpected finding was that, in dr y diglyme, iron borohydride coordination compounds are indefinitely st able and only yield solid Fe2B (or FeB) upon heating. These compounds are probably (L)(n)Fe(BH4)(2) and (L)(n)Fe(BH4)(3) where L = diglyme. Treatment of these complexes in-situ with water causes the precipitati on of Fe2B.