Tris(tetrabutylammonium) hexakis(tert-butanethiolato-κS)hepta-μ3-chlorido-μ3-sulfido-hexamolybdate dihydrate

The octahedral cluster core of the anion in the structure of the title compound, (C16H36N)3[Mo6(C4H9S)6(μ3-Cl)7(μ3-S)]·2H2O, has -3 site symmetry. Two μ3-Cl atoms fully occupy positions in the cluster core, while the remaining six positions are statistically occupied by Cl and S atoms in a 1:5 ratio. The fully occupied Cl-atom positions are located on sites with 3 symmetry, and the N atom of tetrabutylammonium cation is located on a site with 2 symmetry. The structure contains also two disordered solvent water molecules, one of which is located on a threefold rotation axis and the other in a general position, both with an occupancy of 0.25. The water molecules are localized in cavities formed by the tetrabutylammonium cations and the tert-butanethiolate groups. The metal clusters are stacked in a cubic close packing arrangement along [001].

The octahedral cluster core of the anion in the structure of the title compound, (C 16 H 36 N) 3 [Mo 6 (C 4 H 9 S) 6 ( 3 -Cl) 7 ( 3 -S)]Á-2H 2 O, has 3 site symmetry. Two 3 -Cl atoms fully occupy positions in the cluster core, while the remaining six positions are statistically occupied by Cl and S atoms in a 1:5 ratio. The fully occupied Cl-atom positions are located on sites with 3 symmetry, and the N atom of tetrabutylammonium cation is located on a site with 2 symmetry. The structure contains also two disordered solvent water molecules, one of which is located on a threefold rotation axis and the other in a general position, both with an occupancy of 0.25. The water molecules are localized in cavities formed by the tetrabutylammonium cations and the tert-butanethiolate groups. The metal clusters are stacked in a cubic close packing arrangement along [001].

Comment
The octahedral clusters of early transition metals are often regarded as precursors of functional materials with redox and/or luminescent properties. The advantage of halide-bridged clusters [Mo 6 (µ 3 -X) 8 X 6 ] 2-(X = halogen) is the ability of tuning the electronic structure and the properties of the cluster core by step-by-step exchange of the terminal X atoms.
Recently, the reaction of [Mo 6 (µ 3 -X) 8 (OMe) 6 ] 2with excess EtSH was reported leading to the smooth substitution of the terminal methoxides to ethanethiolate groups. The latter can be further substituted by other SRgroups where R = butyl, benzyl or 3-indolyl (Szczepura et al., 2008). Our attempt was aimed to prove if the reaction of [Mo 6 (µ 3 -X) 8 X 6 ] 2with t BuSNa would stop on the substitution of the terminal X atoms, or would result in a core rearrangement as well.
Previously, t BuSwas reported to be the source of the S 2anion (see, for example: Petrov et al. 2010).
The presence of three tetrabutylammonium cations designates the charge of the cluster core. Keeping in mind the high oxidation potential of the [Mo 6 (µ 3 -Cl) 8 Cl 6 ] 3-/2pair (1.53 V in MeCN versus SCE, Nocera & Gray, 1984) one would formulate the cluster core composition as [Mo 6 (µ 3 -S)(µ 3 -Cl) 7 (S t Bu) 6 ] 3-. The analysis of the temperature factors of the atoms in the µ 3 -positions leads us to the conclusion that two positions are occupied with Cl atoms only, while the remaining six positions are statistically occupied with Cl and S atoms in a 1:5 ratio (Fig. 1). The presence of one S atom in the cluster core has no noticeable effect on its geometry (Schoonover et al., 1996;Szczepura et al., 2008).
The structure contains two disordered lattice water molecules. One is located on a threefold rotation axis, the other is

Refinement
The site occupation factors of the S and Cl atoms of the disordered Cl2/S2 site were preliminary refined without any constrains giving us the ratio. Constrained occupation factors were taken into account in the final refinement cycle. The composition of the anion has been confirmed by electrospray mass-spectrometry. The signal at m/z 695.7 was assigned to the [Mo 6 (µ 3 -S)(µ 3 -Cl) 7 (S t Bu) 6 ]] 2anion. The H atoms of the disordered water molecules could not be located and were excluded from refinement.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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 R-factors(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. Hydrogen atoms of water molecules are not located. One of water molecules is disodered by two positions. Hydrogen atoms of cation and anion are placed geometrically.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (