Crystal and molecular structure and properties of ammonium dimolybdate

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.