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

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 Tc=248 K there appears a phase with rank four superspace group P6122(00γ), the one typically observed at room temperature in n-alkane/urea compounds with longer guest molecules. A misfit parameter, defined by the ratio γ=ch/cg (chost/cguest), is found to be 0.632±0.005. Below Tc1=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 P1211(α0γ). We discuss analogies and differences with n-heptane/urea, which also presents a monoclinic, modulated low-temperature phase.
 [1] ;  [1] ;  [1] ;  [2] ;  [3] ;  [3] ;  [4] ;  [5]
  1. Univ. of Rennes, Rennes (France). Inst. of Physics
  2. Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
  3. European Synchrotron Radiation Facility (ESRF), Grenoble (France)
  4. Kansas State Univ., Manhattan, KS (United States). Dept. of Chemistry
  5. Univ. of Rennes, Rennes (France). Campus de Beaulieu, Dept. of Physics
Publication Date:
OSTI Identifier:
Grant/Contract Number:
AC02-06CH11357; CHE-0809845
Accepted Manuscript
Journal Name:
Zeitschrift fuer Kristallographie. Crystalline Materials
Additional Journal Information:
Journal Volume: 230; Journal Issue: 1; Journal ID: ISSN 2194-4946
De Gruyter
Research Org:
Argonne National Laboratory (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE; National Science Foundation (NSF)
Country of Publication:
United States
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY alkane/urea crystals; aperiodic crystals; crystallographic superspace; diffraction; phase transitions