The composition and proposed structure of the alkali metal layered molybdenum bronzes

The chemistry of the layered molybdenum bronzes with alkali metals as the guest cations was investigated. The reaction of MoO3 and dithionete ion, S2O42−, in neutral, buffered solutions resulted in the formation of bronzes, [A+(H2O)n]xMoO3x− where A = Li, Na, K, Rb or Cs, and eliminated the problem of the co-intercalation of adventitious protons. Chemical analysis of these bronzes shoed x to be ∼ 0.25 and thermogravimetric analysis was used to determine the number of intercalated water molecules, n. The interlayer spacings of both air-dried (AD) and vacuum dried (VD) products were measured, and models to account for these spacings were proposed. Electron diffraction from the (hOl) planes of [Na(H2O)2]0.25MoO3 (VD) allowed the powder X-ray diffraction pattern to be indexed on an orthorhombic unit cell with a = 3.876(2), b = 19.093(7) and c = 3.733(3)Å. The systematic absences were consistant with space group Ammm. The powder pattern of the more fully hydrated bronze [Na(H2O)5]o.25MoO3 (AD) was also indexed on a related orthorhombic cell with a = 3.884(1), b = 22.618(8) and c = 3.751(2)Å. The systematic absences in this case are compatable with Cmcm symmetry.