Azide anion encapsulation in a tetraurea receptor

The azide complex [Na(15-crown-5)](2)[L(N-3)(2)] has been synthesized. X-ray single-crystal diffraction analysis revealed that two orthogonally oriented aside anions are encapsulated in one receptor, each by two opposite urea edges of the square tetreurea ligand through N-(urea) - H center dot center dot center dot 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. (C) 2011 Elsevier B.V. All rights reserved.