Distinction between Mn(iii) and Mn(ii) by using a colorimetric chemosensor in aqueous solution

A new colorimetric chemosensor for Mn(iii) and Mn(ii) was developed by combination of 2-(aminomethyl)aniline and 4-(diethylamino)-2-hydroxybenzaldehyde. This sensor 1 exhibited an obvious color change from pale yellow to reddish brown in the presence of Mn³⁺ in aqueous solution (buffer/CH₃CN = 7 : 3), which was reversible with the addition of EDTA. Moreover, 1 could be used to detect and quantify Mn³⁺ in water samples, and as a practical, visible colorimetric test kits for Mn³⁺. Moreover, 1 could detect Mn²⁺via the formation of 1-Mn³⁺ complex with longer reaction time. The resulting different reaction time of Mn(iii) and Mn(ii) with 1 was used to differentiate between Mn(iii) and Mn(ii). Finally, the sensing ability of 1 for Mn³⁺ was supported by theoretical calculations.