A quinoxaline–diaminomaleonitrile conjugate system for colorimetric detection of Cu2+ in 100% aqueous medium: observation of aldehyde to acid transformation

Abstract

In this work, we have strategically incorporated a quinoxaline derivative and a diaminomaleonitrile moiety to construct a chemosensor, 2-amino-3-[(quinoxalin-2-ylmethylene)-amino]-but-2-enedinitrile (H₂qm). The notable feature of this strategy is to generate a highly conjugated Schiff base platform with interesting binding properties. Remarkably, H₂qm exhibited a visual sensing ability towards Cu²⁺ in 100% aqueous medium. The effectiveness of the chemosensor has been demonstrated by utilizing it to determine the Cu²⁺ concentration in real samples. Interestingly, the reaction between H₂qm and Cu(ClO₄)₂·6H₂O in DMSO yielded a quinoxaline-2-carboxylic acid based compound and single crystal X-ray diffraction analysis unveiled the resulting structure as [(qa)₂Cu(H₂O)₂] (Hqa = quinoxaline-2-carboxylic acid).