Bis(hydroxyamino)triazines: Versatile and high-affinity tridentate hydroxylamine ligands for selective iron(iii) chelation

A new versatile family of chelating agents based on bis(hydroxyamino)-1,3,5-triazines, BHTs, is described. The properties of different BHT ligands are determined by electrochemistry, spectroscopy and titrimetry revealing high redox stability, transparency in the visible range, and diprotic acid-like behaviour in the 5–9 pH range. The iron(iii) and iron(ii)–BHT complexes were studied revealing high affinity of BHTs to iron(iii). Electrochemical studies show exceptional preference of the BHT ligands to iron(iii) over iron(ii), this, in addition to their small size and their fast and reversible electrochemistry makes them potentially useful electrochemical redox couples for the low end of the aqueous potential window (<0.6 V, vs. NHE). The synthetic versatility of the new ligands allows easy tuning of the hydrophobicity, redox potential, and to some extent the stability constant of the complexes by alteration of the peripheral groups appended to the BHTs.