Re‐Evaluation of the Applicability of Terpyridine as a Highly Selective Aqueous Colorimetric Sensor for Mercury

In a more than 100-times cited article published in Chem. Eur. J. in 2008 (reference [4]), 2,2´:6´2´´-terpyridine (tpy) has been reported to be a "highly selective colorimetric aqueous sensor for mercury." Verification of this message reveals that the key data and claims reported in the article [4] do not agree with reality. In aqueous DMSO, the reaction of Hg^II compounds with tpy does not produce the pink species [Hg(tpy)₂]²⁺, but white (colorless) products with limited solubility, uncertain stoichiometry and thus structure, and zero use in colorimetry. The color and spectra assigned in the article [4] to Hg^II/tpy systems actually exhibit systems Fe^II/tpy, so that tpy can potentially serve as a colorimetric aqueous sensor for Fe^II ions with the naked-eye detection limit of 1·10^-6 mol/L. Practically only Fe^II mono-tpy species are present in solutions in DMSO(aq) of conc. at least up to the 10^-2 mol/L.