The creation of modulated monoclinic aperiodic composites in n-alkane/urea compounds



Citation: Mariette, C., Guerin, L., Rabiller, P., Chen, Y. S., Bosak, A., Popov, A., . . . Toudic, B. (2015). The creation of modulated monoclinic aperiodic composites in n-alkane/urea compounds. Zeitschrift Fur Kristallographie, 230(1), 5-11. doi:10.1515/zkri-2014-1773
n-Dodecane/urea is a member of the prototype series of n-alkane/urea inclusion compounds. At room temperature, it presents a quasi-one dimensional liquid-like state for the confined guest molecules within the rigid, hexagonal framework of the urea host. At lower temperatures, we report the existence of two other phases. Below T-c=248 K there appears a phase with rank four superspace group P6(1)22(00 gamma), the one typically observed at room temperature in n-alkane/urea compounds with longer guest molecules. A misfit parameter, defined by the ratio gamma=C-h/C-g (C-host/C-guest), is found to be 0.632 +/- 0.005. Below T-c1=123 K, a monoclinic modulated phase is created with a constant shift along c of the guest molecules in adjacent channels. The maximal monoclinic space group for this structure is P12(1)1(alpha 0 gamma). Analogies and differences with n-heptane/urea, which also presents a monoclinic, modulated low-temperature phase, are discussed.


Alkane/Urea Crystals, Aperiodic Crystals, Crystallographic Superspace, Diffraction, Phase Transitions, Urea Inclusion-Compounds