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Redox Properties of C6S8n- and C3S5n- (n = 0, 1, 2):  Stable Radicals and Unusual Structural Properties for C−S−S−C Bonds

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journal contribution
posted on 02.03.2001, 00:00 by Jonathan G. Breitzer, Alex I. Smirnov, Lisa F. Szczepura, Scott R. Wilson, Thomas B. Rauchfuss
The new anionic carbon sulfides C6S102- and C12S162- are described and crystallographically characterized. The C12S162- anion consists of two C6S8 units connected by an exceptionally long (2.157(12) Å) S−S bond. In solution, C12S162- exists in equilibrium with the radical C6S8-•. The equilibrium constant for radical formation (293 K, THF) is 1.2 × 10-4 M, as determined by optical spectroscopy at varying concentrations. Radical formation occurs through scission of the S−S bond. On the basis of variable temperature EPR spectra, the thermodynamic parameters of this process are ΔH = +51.5 ± 0.5 kJ mol-1 and ΔS = +110 ± 3 J mol-1 K-1. C6S102- is an oxidation product of C3S52- and consists of two C3S5 units connected by an S−S bond. The S−S bond length (2.135(4) Å) is long, and the CS−SC torsion angle is unusually acute (52.1°), which is attributed to an attractive interaction between C3S2 rings. The oxidation of (Me4N)2C3S5 occurs at −0.90 V vs Fc+/Fc in MeCN, being further oxidized at −0.22 V. The similarity of the cyclic voltammogram of (Me4N)2C6S10 to that of (Me4N)2C3S5 indicates that C6S102- is the initial oxidation product of C3S52-.