Selective colorimetric sensing and perfect linear recognition of azide: Formation of Cu-azide-Cu cascade complex within the cavity of cryptand

C3V symmetric tripodal molecular pocket for linear anions: Selective colorimetric detection of azide through N4-Cu-π···hole interactions

Tris(3-amino propyl)amine (TRPN) based C₃v symmetric tripodal molecular pocket, L has been prepared and mono copper complex of L, (1) having Cu-N₄-π··· hole as recognizing elements, becoming a potential and selective colorimetric chemo sensor for perfect linear recognition of N₃^-, generate a Cu-NNN- π··· hole unit inside the tripodal pocket. Systematic spectrometric and naked-eye colorimetric studies reveal that, this chemo sensor is also colorimetrically recognizing the cyanide ion by its cavity via Cu-N₄-π···hole interactions; nevertheless, when azide anion is entering as a guest into the molecular pocket of 1 which is already hosted cyanide anion, then host displaces cyanide ion, subsequently azide is getting inside the cavity. The strength of the copper complex, 1 towards azide and cyanide are found to be 2.36 × 10³M^-1, and 1.87 × 10³ M^-1 respectively in 7:3 acetonitrile:water solvent medium. Further, the ability of cyanide displacement by azide in complex 1 is found to be 2.53 × 10³ M^-1. To the best of our knowledge, this is the first example of naked-eye detection of azide via cyanide displacement assay by a tripodal receptor.