Azide anion encapsulation in a tetraurea receptor

The azide complex [Na(15-crown-5)]2[L(N3)2] has been synthesized. X-ray single-crystal diffraction analysis revealed that two orthogonally oriented azide anions are encapsulated in one receptor, each by two opposite urea edges of the square tetreurea ligand through N(urea) − H⋯N(azide) hydrogen bonding. UV–vis titration confirmed the 1:2 (host/guest) binding mode in solution with slight bathochromic shifts compared to the ligand.