Isomers among the carbon sulfides C4S6—synthesis and crystal structures of α,α-C4S6, α,β-C4S6, and of a second polymorph of the diiodine adduct α,β-C4S6·I2

Dalton Transactions Pub Date: 2005-11-14 DOI: 10.1039/B511746A

Abstract

The reaction of the α and β forms of C3S52? with thiophosgene yields two isomeric carbon sulfides α,α-C4S6 and α,β-C4S6, respectively. The crystal structures of both compounds could be determined for the first time. Both structures are made up of almost planar molecules. The α,α-isomer (1,3-dithiolo-(4,5-d)-1,3-dithol-2,5-dithione) is D2h-symmetric, while the α,β-isomer is approximately Cs-symmetric. In the molecules of both isomers the two different C3S5 units are retained without significant alterations of structural parameters. α,α-C4S6 is unstable with respect to α,β-C4S6. The molecular rearrangement can be induced by a short thermal treatment at 150 °C. Significant differences are found in the mass spectra fragmentation patterns. Only α,β-C4S6 shows an intense signal for C3S2+ and is therefore a potential source for the synthesis of carbon subsulfide via flash vacuum pyrolysis. Only α,β-C4S6 forms a stable adduct with I2. α,β-C4S6·I2 was already known (F. L. Lu, K. M. Keshavarz-K, G. Srdanov, R. H. Jacobson and F. Wudl, J. Org. Chem., 1989, 54, 2165, ), but a second polymorph is formed on crystallisation from a different solvent. The two polymorphic forms do not show differences in the structures of the individual molecules but show a different packing pattern. α,β-C4S6·I2 is remarkably thermally stable. Thermal analysis shows that I2 cleavage occurs in that temperature region above 200 °C when C–S bonds are broken and CS2 and I2 are simultaneously liberated. Performed at 270 °C thermolysis of α,β-C4S6·I2 yields under cleavage of I2 and CS2 a black polymeric carbon sulfide (CS)x which is probably a mixture of graphitic carbon and unidentified amorphous polymeric carbon sulfides.

Graphical abstract: Isomers among the carbon sulfides C4S6—synthesis and crystal structures of α,α-C4S6, α,β-C4S6, and of a second polymorph of the diiodine adduct α,β-C4S6·I2
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