SYNTHETIC, STRUCTURAL AND SPECTROSCOPIC STUDIES OF THE DONATING PROPERTIES OF SULFUR-RICH MOLECULES TOWARDS I-2 - X-RAY STRUCTURE OF 1,3-DITHIOLE-2-THIONE.DIIODINE

A study on the 1:1 complex between I2 and 1,3-dithiole-2-thione (dtlt) in CHCl3 solutions and in the solid state is reported. The refined formation constants (K20-degrees = 89 +/- 1 mol-1 dm3) and molar extinction coefficients have been calculated simultaneously in the 260-550 nm range by means of a general computer program. The enthalpy change (DELTAH-degrees = -9.66 +/- 0.01 Kcal mol-1) falls in the range of moderately-strong thione donors. The features of the u.v.-vis. spectrum indicate that the complex is of charge-transfer type. The 1:1 complex has been isolated in the solid state and IR spectroscopic results suggest the thione sulphur donation. FT-Raman spectra on this solid compound show a very strong band attributed to nu(I-I) at 143 cm-1. An X-rav structure of dtlt.I2 has shown that the crystals are orthorhombic, space group P2(1)2(1)2(1), a = 11.413 (7), b = 10.038 (7), c = 7.760 (6) angstrom, V = 889.0 (1.1) angstrom3, Z = 4. Solution and refinement of intensity data gave final residuals of R = 0.0537. A comparison with the donor behaviour of 1,3-dithiolane-2-thione shows that while in solution dtlt has values of K and enthalpy change higher than those found in the dtt case, in the solid state the more significant bond distances and angles are very similar.