F. Cristiani, F. Demartin, F. A. Devillanova, F. Isaia, V. Lippolis, G. Verani Spectroscopic studies of charge-transfer complexes of 1,4,7-trithiacyclononane with diiodine.

1,4,7-Trithiacyclononane ([9]aneS3) reacts with molecular diiodine in CH2Cl2 to form a 1:1 adduct. The formation constant and the thermodynamic parameters of this adduct have been determined by UV-visible spectra of several solutions at the temperatures of 15, 20, 25, 30, and 35-degrees-C. The C-13 NMR spectra show that adducts with higher ligand/diiodine molar ratios are formed. Two neutral charge-transfer molecular compounds having formula 2[9]aneS3 . 4I2 (I) and [9]aneS3 . 3I2 . (II) have been obtained as crystals. The crystals of I are triclinic (a = 8.498(2) angstrom, b = 13.984(4) angstrom, c = 14.898(6) angstrom, alpha = 65.57(2)degrees, beta = 89.19(2)degrees, gamma = 81.26(2)degrees, Z = 2, space group P1BAR; R = 0.025) and contain units formed by two [9]aneS3 molecules connected by a diiodine molecule; one [9]aneS3 binds two other diiodine molecules, while the second binds only one other diiodine molecule. The crystals of II are monoclinic (a = 13.810(2) angstrom, b = 9.829(4) angstrom, c = 16.198(6) angstrom, beta = 113.41(2)degrees, Z = 4, space group P2(1)/c; R = 0.019) and contain molecules of [9]aneS3 binding three diiodine molecules. FT-Raman spectra in the characteristic nu(I-I) region, carried out on the solid adducts, are discussed in comparison with the structural parameters