Fluoroformyl Trifluoroacetyl Disulfide, FC(O)SSC(O)CF3: Synthesis, Structure in Solid and Gaseous State and Conformational Properties

ERBEN, M. F.; DELLA VÉDOVA,C. O.; WILLNER, H.; TRAUTNER, F.; OBERHAMMER, H.; BOESE, R.

INORGANIC CHEMISTRY

American Chemical Society

Lugar: Columbus, OH, 43210, USA; Año: 2005 vol. 44 p. 7070 - 7077

0020-1669

Fluoroformyl trifluoroacetyl disulfide, FC(O)SSC(O)CF3, is prepared by quantitative reaction between FC(O)SCl and CF3C(O)SH. The conformational properties and geometric structure of the gaseous molecule have been studied by vibrational spectroscopy (IR(gas), Raman(liquid), IR(matrix)), gas electron diffraction (GED), and quantum chemical calculations (B3LYP and MP2 methods). The disulfide bond length derived from the GED analysis amounts 2.023(3) Å, and the dihedral angle around this bond, d(CS-SC), is 77.7(21)°, being the smallest dihedral angle measured for noncyclic disulfides in the gas phase. The compound exhibits a conformational equilibrium at room temperature having the most stable form C1 symmetry with a synperiplanar (sp-sp) orientation of both carbonyl groups with respect to the disulfide bond. A second form was observed in IR spectra of the Ar matrix isolated compound at cryogenic temperatures, corresponding to a conformer that possess the carbonyl bond of the FC(O) moiety in antiperiplanar position with respect to the S-S single bond (ap-sp). A ¢H° ) H°(ap-sp) - H°(sp-sp) ) 1.34(11) kcal/mol has been determined by IR(matrix) spectroscopy. The structure of single crystal of FC(O)SSC(O)CF3 was determinate by X-ray diffraction analysis at low temperature using a miniature zone melting procedure. The crystalline solid (monoclinic, P21/ n, a= 5.240(4)Å, b= 23.319(17)Å, c= 6.196(4)Å, a= 113.14(3)°) consists  exclusively of the (sp-sp) conformation. The geometrical parameters agree with those obtained for the molecule in the gas phase.