Urea inclusion compounds

Abstract In these compounds the ‘host’ substructure consists of an open framework of hydrogen-bonded urea molecules, in which exist parallel one-dimensional tunnels of diameter about 5.5 – 6 Å that accommodate ‘guest’ molecules such as the n-alkanes or similar long-chain molecules. A description is given of how diffuse X-ray scattering in conjunction with Monte Carlo (MC) computer simulation can be used to investigate guest-host interactions, with particular reference to n-hexadecane-urea (HD-urea) and 1,10-dibromo-n-decane-urea (DBD-urea). The MC modeling identified the origins of different features of the diffraction patterns. Along the channels the alkanes form a pseudo 1D crystal. There is short-range order between the orientations of molecules in neighbouring channels that leads to a phase transition in which ordered domains are formed. (119 words)