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(diglyme) by NaBH4 has been investigated with mechanistic and stoichiometric factors in mind. The bewildering complexity of such reactions has been partly alleviated. We find that the primary products are different depending on the reaction medium. In aqueous solution Fe2+ yields mainly 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 dry diglyme, iron borohydride coordination compounds are indefinitely stable 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 precipitation of Fe2B.