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 13C NMR study

Equilibrium constants (K) and thermodynamic parameters for the charge-transfer complexes between diiodine and Delta(3)-4-S-methyl-5,5-dimethylimidazolidine-2-thione (1), 2-S-methyl-5,5-dimethylimidazolidine-4-thione (2), and Delta(1)-Delta(3)-2S-methyl-4-S-methyl-5,5- dimethylimidazolidine (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) mol(-1), 25 degrees C, respectively) owing to the presence of a thioamidic group in the molecule, whereas in compound 3, the N-coordination causes a strong reduction of the formation constant (K = 14.6 +/- 0.8 dm(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 for 1. Additional spectroscopic data (FT-Raman, NMR) enables a deeper understanding of the mutual interaction between donors and diiodine.