Based on Job plot and ESI-mass data analysis, we propose that the two oxygen atoms and the imine nitrogen of 1 might bind to Cu2þ and the remaining site of the 1eCu2þ complex may be occu- pied by a nitrate anion (Scheme 3). The coordination of nitrate ions was previously proposed when chemosensors were bound to Cu2þ with a 1:1 stoichiometry in organic solvents.