Redetermination of diammonium thiomolybdate

In contrast to the previous structure determinations of the title structure, (NH4)2[MoS4], the present determination at 173 K localized the positions of the H atoms. The title structure belongs to the β-K2SO4 family and all the ions are located on crystallographic mirror planes. The ions are held together by N—H⋯S hydrogen bonds (some of which are bifurcated), forming a three-dimensional network. One of the N atoms has nine contacts to the S atoms shorter than 4 Å, and the other has ten.

In contrast to the previous structure determinations of the title structure, (NH 4 ) 2 [MoS 4 ], the present determination at 173 K localized the positions of the H atoms. The title structure belongs to the -K 2 SO 4 family and all the ions are located on crystallographic mirror planes. The ions are held together by N-HÁ Á ÁS hydrogen bonds (some of which are bifurcated), forming a three-dimensional network. One of the N atoms has nine contacts to the S atoms shorter than 4 Å , and the other has ten.

Related literature
For preparation of the title compound, see: Herzog et al. (1981). For structures of the -K 2 SO 4 family, see: Fá bry & Pé rez-Mato (1994). For other structure determinations of the title compound, see: Lapasset et al. (1976); Schä fer et al. (1964). For a description of the Cambridge Structural Database, see: Allen (2002).
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: FB2179).
the two previous structure determinations did not include the positions of the H atoms.
The crystal structure belongs to the β-K 2 SO 4 family (Fábry & Pérez-Mato, 1994). The anions and cations are held together by N-H···S hydrogen bonds forming a three-dimensional network involving all H atoms.

Experimental
The ammonium tetrathiomolybdate (NH 4 ) 2 MoS 4 was synthesized by the reaction from (NH 4 )  4H 2 O in 50 ml aqueous ammonia. At first the reaction solution became yellow then the colour changed from yellow towards red. The red colour indicated the end of the reaction (Herzog et al., 1981). X-ray quality crystals of (NH 4 ) 2 MoS 4 were grown from the reaction solution at ambient temperature. The crystals are pleochroic, changing colour from red to green according to the view angle.

Refinement
Hydrogen atoms were located in a difference Fourier map and refined isotropically. The N-H distances were restrained to 0.878 (20) Fig. 1. A view of the three molecules in the asymmetric unit of the title compound, with the atom-numbering scheme. The displacement ellipsoids are drawn at the 50% probability level and the H atoms are shown as small spheres of arbitrary radii. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.