Pressure-tuning Raman spectra of diiodine thioamide compounds: models for antithyroid drug activity

The pressure-tuning Raman spectra of five solid, diiodine heterocyclic thioamide compounds (mbztS)I(2) (mbztS = N-methyl-2-mercaptobenzothiazole) (1); [(mbztS)(2)I](+)[I(7)](-) (2); (pySH)I(2) (pySH = 2-mercaptopyridine) (3); [(pySH)(pyS](+)[I(3)](-) (4); (thpm)(I(2))(2) or possibly [(thpm)I(2)](+)[I(3)](-) (thpm = 2-mercapto-3,4,5,6-tertahydropyrimidine (5) have been measured for pressures up to approximately 50 kbar using a diamond-anvil cell. Compounds 1, 4, and 5 undergo pressure-induced phase transitions at approximately 35, approximately 25, and approximately 32 kbar, respectively. Following the phase transition in 1, the pressure dependences of the vibrational modes, which were originally located at 84, 111, and 161 cm(-1) and are associated with the S(cdots, three dots, centered)I-I linkage, are 2.08, 1.78, and 0.57 cm(-1)/kbar, respectively. These pressure dependences are typical of low-energy vibrations. The pressure-tuning FT-Raman results for the pairs of compounds 1 , 2, 3, and 4 are remarkably similar to each other suggesting that the compounds are most probably perturbed diiodide compounds rather than ionic ones. The Raman data for 5 show that it is best formulated as (thpm)(I(2))(2) rather than [(thpm)(2)I](+)[I(3)](-).