A colorimetric chemosensor for both fluoride and transition metal ions based on dipyrrolyl derivative.

The synthesis, characterization and ion binding studies of 2,3-di(1H-2-pyrrolyl)pyrido[2,3-b]pyrazine (1) have been described. 1, which has been targeted with a view to sensing both F- and transition metal ions, exhibits binding-induced color changes from yellowish green to red/brown observable by the naked eye. The binding site for the metal ion in the system has been unambiguously established by single-crystal X-ray diffraction study of a Ni(II) complex of 1. While the estimated value of the binding constant of 1 with F- is 4.9 x 10(3) M(-1), the binding constants for the cations are found to be two orders higher in magnitude in acetonitrile. Even though 1 possesses two separate binding sites for F- and metal ions, it is shown that the presence of the cation influences the binding of the anion and vice versa. The binding constant values of an ion in the presence of oppositely charged species are measured to be significantly lower.