title: Confined linear molecules inside an aperiodic supramolecular crystal: the sequence of superspace phases in n-hexadecane/urea.
abstract: High-resolution studies of the host-guest inclusion compound n-hexadecane/urea are reported at atmospheric pressure, using both cold neutrons and x-ray diffraction. This intergrowth crystal presents a misfit parameter, defined by the ratio c(h)/c(g) (c(host)/c(guest)), which is temperature independent and irrational (γ = 0.486 ± 0.002) from 300 to 30 K. Three different structural phases are reported for this aperiodic crystal over this temperature range. The crystallographic superspaces are of rank 4 in phases I and II, whereas phase III is associated with an increase in rank to 5, with a supplementary misfit parameter (δ = 0.058 ± 0.002) that is constant throughout this phase. The superspace group of phase I is hexagonal P6(1)22(00γ) down to T(c1) = 149.5 ± 0.5 K; phase II, which persists down to T(c2) = 127.8 ± 0.5 K is orthorhombic P2(1)2(1)2(1)(00γ), and phase III is orthorhombic P2(1)2(1)2(1)(00γ)(00δ).
authors: Institut de Physique de Rennes, UMR UR1-CNRS 6251, Université de Rennes 1, 35042 Rennes, France.
authors: M
authors: M
authors: Huard
authors: B
authors: B
authors: Toudic
authors: P
authors: P
authors: Rabiller
authors: C
authors: C
authors: Ecolivet
authors: L
authors: L
authors: Guérin
authors: P
authors: P
authors: Bourges
authors: T
authors: T
authors: Breczewski
authors: Mark D
authors: MD
authors: Hollingsworth
mesh_terms: D000473:Alkanes / Q000737:chemistry*; D003460:Crystallization; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D013696:Temperature; D014508:Urea / Q000737:chemistry*
chemical_list: D000473:Alkanes; D014508:Urea; C007932:n-hexadecane