Crystalline Complexes of N,N′-Ditritylurea (DTU) and N-Tritylurea (NTU) Hosts with Molecular Guests

Abstract

This paper reports crystalline complexes of the new hosts N,N′-ditritylurea (DTU) and N-tritylurea (NTU) with various uncharged molecular guests. The crystal structures of the following complexes were elucidated by single crystal X-ray diffraction analysis at 115°K: (I) 1:1 DTU-propanamide — space group C2/c, a=15.839A, b=9.088A, c=24.584A, β=111.05°, Z=4; (II) 1:1 DTU-ethyl N-acetylglycinate — space group \(P\bar 1\),a=9.010A, b=10.800A, c=l9.810 A, α=105.29°, β=94.33°, γ=93.03°, Z=2; (III) 2:1 NTU-N,N-dimethyIformamide — space group Cc, a=29.614A, b=8.906A, c=16.127A, β=121.04°, Z=4. The three crystal structures are stabilized mainly by a cooperative effect of hydrogen bonding between amide fragments displaced along the shortest axis of each crystal. This interaction occurs between host and guest in complexes I and II, and between host and host in complex III. The latter also represents a cage-type clathrate in which the guest molecules are accommodated in voids between the hydrophobic fragments of four neighboring NTU hosts. On the other hand, complexes of DTU are characterized by a more specific interaction between the two components, each guest molecule being inserted between two adjacent hosts (related by translation) and strongly bound to them via hydrogen bridges. These results illustrate a useful concept in the design of molecular species which can be potential hosts upon crystallization with neutral molecular guests.