ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

3,5-Bis(2-hydroxyphenyl)-1 H -1,2,4-triazole based ligands — protonation and metal complex formation

Stefan Stucky, Nadine J. Koch, Uwe Heinz, and Kaspar Hegetschweiler

Anorganische Chemie, Universität des Saarlandes, Postfach 151150, 66041 Saarbrücken, Germany

E-mail: hegetschweiler@mx.uni-saarland.de

Received: 30 October 2007  Revised: 14 January 2008  Accepted: 16 January 2008

Abstract: 3,5-Bis(2-hydroxyphenyl)-1H-1,2,4-triazole (H₂L^a) and 4-[3,5-bis(2-hydroxyphenyl)-1H-1,2,4-triazol-1-yl]benzoic acid (H₃L^b) have been prepared, and crystal structure of the intermediate 2-(2-hydroxyphenyl)-4H-1,3-benzoxazin-4-one has been determined. Temperature dependent ¹H NMR spectroscopic measurements of H₂L^a indicated dynamic behavior with the equilibrium between the two asymmetric tautomers. For H₃L^b, pD-dependent ¹H NMR spectroscopic measurements showed small but characteristic shifts in the range of 0 ≤ pD ≤ 1, indicative of a triazole nitrogen atom protonation; the corresponding pK _a of 0.98 ± 0.04 was determined by spectrophotometric titrations. (H₂O, 26°C, 1 M KCl/HCl). Formation of [Fe^III(L^a)]⁺ (pH 2.5) and [Fe^III(L^a)₂]⁻ (pH > 6) was verified by UV-Vis spectroscopy. Complex formation of H₃L^b with Al³⁺ and VO²⁺ was investigated by ¹H NMR spectroscopic titration and cyclic voltammetry, respectively. Single crystals of the phenoxo bridged [V^VO(HL^b)(EtO)]₂·2EtOH were characterized by X-ray structural analysis.

Keywords: tridentate ligand - deferasirox - iron - aluminum - vanadium

Full paper is available at www.springerlink.com.

DOI: 10.2478/s11696-008-0043-x

Chemical Papers 62 (4) 388–397 (2008)