Redetermination of di-μ-sulfido-bis{[(2R)-2-acetoxy-2-aminoethane-1-thiolato-κ2 N,S]oxidomolybdenum(V)}

The structure of the title compound, [Mo2(C4H8NO2S)2O2S2], has been redetermined. Besides obvious differences between the original [Drew & Kay (1971 ▶). J. Chem. Soc. A, pp. 1851–1854] and the current unit-cell parameters, some packing features of the structure are also different; these findings are the result of significant improvements in the precision and accuracy of the present structure analysis. The two Mo atoms in the dimeric complex have very similar distorted trigonal–bipyramidal environments. Each Mo atom is bonded to an S atom and to an N atom of an l-cysteine ester ligand, to a terminal O atom and to two S atoms which bridge to the adjacent Mo atom [Mo⋯Mo separation = 2.8191 (2) Å]. N—H⋯Ocarbonyl and N—H⋯Oterminal hydrogen-bonding interactions consolidate the crystal packing. During the synthesis, the originally employed l-cysteinate ligand has been converted to the l-cysteinate methyl ester ligand. Since this reaction does not take place without tin(IV) chloride, it is clear that tin(IV) chloride acts as a catalyst for the reaction.

The structure of the title compound, [Mo 2 (C 4 H 8 NO 2 S) 2 O 2 S 2 ], has been redetermined. Besides obvious differences between the original [Drew & Kay (1971). J. Chem. Soc. A, pp. 1851-1854] and the current unit-cell parameters, some packing features of the structure are also different; these findings are the result of significant improvements in the precision and accuracy of the present structure analysis. The two Mo atoms in the dimeric complex have very similar distorted trigonalbipyramidal environments. Each Mo atom is bonded to an S atom and to an N atom of an l-cysteine ester ligand, to a terminal O atom and to two S atoms which bridge to the adjacent Mo atom [MoÁ Á ÁMo separation = 2.8191 (2) Å ]. N-HÁ Á ÁO carbonyl and N-HÁ Á ÁO terminal hydrogen-bonding interactions consolidate the crystal packing. During the synthesis, the originally employed l-cysteinate ligand has been converted to the l-cysteinate methyl ester ligand. Since this reaction does not take place without tin(IV) chloride, it is clear that tin(IV) chloride acts as a catalyst for the reaction.

Experimental
Crystal data [Mo 2 (C 4 H 8 , 1996); software used to prepare material for publication: Crystal-Structure.

Comment
Molybdenum complexes with sulfur ligands including L-cysteine or L-cysteine ethers are of interest in relation to redoxactive molybdo-enzymes (Newton et al., 1980). Doubly sulfur-bridged molybdenum(V) compounds are prepared and examined as catalysts for redox reactions (Ueyama et al., 1982). The formation of the title compound, C 8 H 16 Mo 2 N 2 O 6 S 8 , (I), has been reported previously in the reaction of sodium molybdate with hydrogen sulphide and L-cysteine methyl ester (Kay & Mitchell, 1970). However, the direct formation of (I) from Na 2 [Mo 2 O 2 S 2 (L-cys) 2 ] (Shibahara & Akashi, 1992) has not been reported previously. In this reaction in methanol, the L-cysteinato ligand has changed to the L-cysteinato methyl ester ligand.

Refinement
The positions of all H atoms were initially located from difference maps and were refined by using the riding model. The isotropic displacement parameters for these atoms were fixed at 1.2 times the equivalent isotropic displacement parameter of their carrier atom.
supplementary materials sup-2 Figures Fig. 1. Molecular configuration and atom-numbering scheme for compound (I) with displacement ellipsoids drawn at the 50% probability level.

Special details
Refinement. Refinement was performed using all reflections. The weighted R-factor (wR) and goodness of fit (S) are based on F 2 . Rfactor (gt) are based on F. The threshold expression of F 2 > 2.0 σ(F 2 ) is used only for calculating R-factor (gt).