The pressure-tuning Raman spectra of five solid, diiodine heterocyclic thioamide compounds (mbztS)I2 (mbztS = N-methyl2-mercaptobenzothiazole) (1); [(mbztS)2I] [I7] − (2); (pySH)I2 (pySH = 2-mercaptopyridine) (3); [(pySH)(pyS] [I3] − (4); (thpm)(I2)2 or possibly [(thpm)I2] [I3] − (thpm = 2-mercapto-3,4,5,6-tertahydropyrimidine (5) have been measured for pressures up to ∼ 50 kbar using a diamond-anvil cell. Compounds 1, 4, and 5 undergo pressure-induced phase transitions at ∼ 35, ∼ 25, and ∼ 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 SI–Ilinkage, 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)(I2)2 rather than [(thpm)2I] [I3] −.