Crystal engineering of urea a-network via I•••O2N synthon and design of SHG active crystal N-4-iodopheny-N′-4′-N′-nitrophenylurea

Crystalline nitrodiphenyl ureas adopt the N-H...O tape alpha-network only when stabilization accrues from the I...O2N or Cequivalent toC-H...O2N synthon, otherwise the urea...nitro motif is preferred; soft, weak interactions can direct polar self-assembly in strong N-H...O hydrogen-bonded crystals.