The crystal structure of (NH 4 ) 2 [Mo 2 (S 2 ) 6 ].8/3H 2

The black crystal of (NH 4 )[Mo 2 (S 2 ) 6 ]* 8/3 H 2 O belongs to the orthorhombic system, space group D 3 2 ‐P22 1 2 1 , with a = 12.064(6), b = 12.534(4), c = 19.558(9)Å, V =2957(3)Å 3 , Z = 4 and D c = 2.23g.cm −3 . The intensity data were collected on a Syntex R3 four‐circle diffractometer. The structure was solved by Patterson method and direct method, the light atoms (except H atoms) were obtained from ΔF syntheses. The structure was refined by least‐squares with anisotropic thermal parameters. The values of R and R w were 0.092 and 0.072 respectively. The crystal structure contains discrete dimeric cluster [Mo 2 (S 2 ) 6 ] 2− ions, NH 4 + cations and H 2 O molecules. There are two crystallographically independent [Mo 2 S 2 ) 6 ] 2− ions in the crystal, one locates on general position [Figure 1(a)], the other locates on two‐fold axis [Figure 1(b)]. It contains one and a half [Mo 2 S 2 ) 6 ] 2− ions in an asymmetric unit. In [Mo 2 S 2 ) 6 ] 2− each Mo is coordinated side on by four S 2 2− groups in a distorted dodecahedral arrangement, two of which are bridging and the other two are terminal. The MoS bond length is 2.441 Å (mean), and SS is 2.049 Å (mean). The MoMo distance is 2.784 Å (mean), which is to be regarded as a single bond length. The formal oxidation state of Mo is five, it is probably a mixed valence Mo IV Mo VI , and so shows a remarkable deep colour.