CHARGE-TRANSFER COMPLEXES BETWEEN SOME S-METHYLATED DERIVATIVES OF 5,5-DIMETHYL-2,4-DITHIOHYDANTOIN AND MOLECULAR DIIODINE - A UV-VISIBLE, IR, FT-RAMAN, AND C-13 NMR-STUDY

Equilibrium constants (K) and thermodynamic parameters for the charge- transfer complexes between diiodine and a(3)-4-S-methyl-5,5-dimethylim idazolidine-2-thione (1), 2-S-methyl-5,5-dimethylimidazolidine-4-thion e (2), and Delta(1)-Delta(3)-2S-methyl-4-S-methyl-5,5- dimethylimidazo lidine (3) have been determined in CH2Cl2 by UV-Visible spectroscopy. Depending on the solvent polarity, compound 2 exists as a Delta(1) or Delta(2) tautomer; both the tautomers are present in CH2Cl2. Compounds 1 and 2 act as good donors (K = 11,000 +/- 800 and 640 +/- 21 dm(3) m ol(-1), 25 degrees C, respectively) owing to the presence of a thioami dic group in the molecule, whereas in compound 3, the N-coordination c auses a strong reduction of the formation constant (K = 14.6 +/- 0.8 d m(3) mol(-1), 25 degrees C). The high difference between the stability constants of 1 and 2 has been ascribed to an intramolecular hydrogen bonding between NH and the bonded iodine, which can be possible only f or 1. Additional spectroscopic data (FT-Raman, NMR) enables a deeper u nderstanding of the mutual interaction between donors and diiodine.