Potentiometric study of equilibrium constants of a novel triazine--thione derivative and its stability constants with Hg^{2+}, Cu^{2+}, Ni^{2+}, Pb^{2+}, and Zn^{2+} metal ions in ethanol and water mixed

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^{2+}, Ni^{2+}, Cu^{2+}, Pb^{2+}, and Zn^{2+} ion complexes were studied in 20% ethanol and water mixed at 25 pm 0.1 °C and ionic strength (I) of 0.1 M supported by NaCl. Four pK_a 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, MH_2L, MH_3L, MH_4L, and MH_{-2}L between Hg^{2+}, Ni^{2+}, Cu^{2+}, Pb^{2+}, and Zn^{2+} ions and HPT. According to the potentiometric and spectrophotometric results, the HPT and Hg^{2+} combination formed a selective and highly stable complex at pH 7.