Potentiometric study of equilibrium constants of a novel triazine–thione derivative and its stability constants

The deprotonation constants of 5-hydroxy-5,6-di-pyridin-2-yl-4,5-dihydro-2H-[1,2,4] triazine-3-thione (HPT) and the stability constants of its Hg , Ni , Cu , Pb , and Zn ion complexes were studied in 20% ethanol and water mixed at 25 ± 0.1 ◦C and ionic strength (I) of 0.1 M supported by NaCl. Four pKa values of HPT were determined: 3.58, 6.30, 9.23, and 9.69. In various pH conditions, the different complex forms were formulated as ML, MHL, MH2L, MH3L, MH4L, and MH−2L between Hg 2+ , Ni , Cu , Pb , and Zn ions and HPT. According to the potentiometric and spectrophotometric results, the HPT and Hg combination formed a selective and highly stable complex at pH 7.