THERMODYNAMIC STUDY ON TRIAZOLO-TRIAZOLE HETEROCYCLIC SYSTEMS

Acid-base properties and complex formation with metal ions of four new triazolo[3,2-c]triazoles (Scheme) having substituents of different electronic character on the bicycle have been investigated at 25 °C in NaCl 0.5 M, as ionic medium, by using potentiometry, polarography and UV-Vis spectrometry (absorption and emission). The pH investigated spans between 0.5 and 12.The study indicated that the neutral heterobicycle (HL) has acid-base properties strongly influenced by the presence of electron withdrawing or releasing groups at position 7 (it can deliver the H+ to form the conjugated base L- and can accept up to two protons, forming the species H2L+ and H3L++). By varying the groups attached at the heterocycle, a remarkable shift of pKa values, up to 5–6 units, is observed. The formation of the cationic species is accompanied by complex tautomeric switchings as shown by single crystal X-ray analysis and theoretical calculations3,4. The excited-state proton transfer also is influenced by the presence of electron withdrawing or releasing groups at position 7. Evidence of the formation of Me(II)-HL, mononuclear complexes, has also been obtained. 1] C-H Zhou, Y. Wang, Current Medicinal Chemistry, 19, N.2 (2012) 239-280. [2] Y. Murti at all, American Journal of Chemistry, 1 (211) 42-46. [3] R. Centore, S. Fusco, A. Capobianco, V. Piccialli, S. Zaccaria, and A. Peluso European Journal of Organic Chemistry, 18 (2013) 3721-3728. [4] R. Centore, C.Manfredi, C.Maglione, A.Carella, A.Capobianco, A.Peluso, D.Colonna, A.Di Carlo, J.of Molecular Structure, 1093 (2015) 119-124