Crystal and molecular structure and properties of ammonium dimolybdate

Authors:
  • AAAlan W. Armour
    Alan W. Armour
  • MDMichael G. B. Drew
    Michael G. B. Drew
  • PMPhilip C. H. Mitchell
    Philip C. H. Mitchell
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Abstract
Crystals of ammonium dimolybdate are triclinic, space group P, Z= 2 with cell dimensions a= 7.937(7), b= 7.305(7), c= 7.226(8)Å, α= 93.88(12), β= 114.33(7), γ= 82.58(13)°. The structure was solved by Patterson and Fourier methods from diffractometer data and refined by least-squares techniques to R 0.066 for 988 reflections. The structure is isomorphous with that of potassium dimolybdate and different from that of sodium dimolybdate. It consists of infinite chains of edge-shared [MoO6] octahedra with adjacent pairs linked by [MoO4] tetrahedra. Ammonium ions occupy interchain positions. Its properties and spectra are compared with those of ammonium heptamolybdate. Dissolution of ammonium dimolybdate in water and its thermal decomposition are discussed.