Average structure of the composite crystal urea/octanedioic acid at room temperature within the superspace formalism.

The average structure of the composite urea/octanedioic acid has been refined using the superspace formalism [superspace group H'3(1)21(00gamma)001;]. Modulation effects seem to be almost negligible. The guest substructure appears to be largely disordered and has been modelled using rigid units occupying 12 equiprobable different orientations inside the urea tunnels. Guest molecules are slightly tilted with respect to the tunnel axis favouring a stronger guest-guest intratunnel interaction.