Synthesis, spectroscopic investigation, x-ray analysis, and structure of 3,4-dibromo- and 3,4-diiodo-1,2,5-thiadiazoles

Abstract

The 1,2,5-thiadiazole moiety serves as a valuable structural component in a diverse array of compounds and polymers, and small halogen-substituted derivatives may act as precursors in their synthesis. This study reports the first synthesis of 3,4-dibromo-1,2,5-thiadiazole (1) and 3,4-diiodo-1,2,5-thiadiazole (2), which were systematically characterized using mid-IR, Raman, UV–Vis, NMR, mass, and He I photoelectron spectroscopies. These analyses offered a comprehensive examination of the electronic and vibrational properties of the compounds. Vibrational spectroscopy indicates that solids 1 and 2 contain multiple crystalline phases. The solid-phase structure of 1 was determined using single-crystal X-ray diffraction. Depending on recrystallization conditions, 1 solidifies in either the triclinic P-1 or monoclinic P2/c space groups. 1 has sufficiently high vapor pressure for studying its thermal stability and decomposition in the gas-phase. Flash vacuum thermolysis of this compound yields quantitatively BrCN, NCCN, Br₂, and sulfur above 800 °C. Additionally, a synthetic method for the novel 3-bromo-4-iodo-1,2,5-thiadiazole (3) has been established.

Graphical abstract