Structural aspects of urea inclusion compounds and their investigation by X-ray diffraction: a general discussion

1990 ◽  
Vol 86 (17) ◽  
pp. 2985 ◽  
Author(s):  
Kenneth D. M. Harris ◽  
John M. Thomas
Keyword(s):  
Inclusion Compounds ◽  
X Ray Diffraction ◽  
X Ray ◽  
Urea Inclusion Compounds ◽  
Urea Inclusion ◽  
Structural Aspects

Structural properties of the guest species in diacyl peroxide/urea inclusion compounds: an X-ray diffraction investigation

1990 ◽  
Vol 431 (1882) ◽  
pp. 245-269 ◽  
Keyword(s):  
Single Crystal ◽  
Structural Properties ◽  
Inclusion Compounds ◽  
X Ray Diffraction ◽  
Channel Axis ◽  
Guest Molecules ◽  
X Ray ◽  
Urea Inclusion Compounds ◽  
Diacyl Peroxide ◽  
Urea Inclusion

In this paper we report single crystal X-ray diffraction studies of urea inclusion compounds containing diacyl peroxides (dioctanoyl peroxide (OP), diundecanoyl peroxide (UP), lauroyl peroxide (LP)) as the guest component. In these inclusion compounds, the host (urea) molecules crystallize in a hexagonal structure that contains linear, parallel, non-intersecting channels (tunnels). The guest (diacyl peroxide) molecules are closely packed inside these channels with a periodic repeat distance that is incommensurate with the period of the host structure along the channel axis. Furthermore, there is pronounced inhomogeneity within the guest structure: within each single crystal, there are regions in which the guest molecules are three-dimensionally ordered, and other regions in which they are only one-dimensionally ordered (along the channel axis). Although it has not proven possible to ‘determine’ the guest structures in the conventional sense, substantial information concerning their average periodicities and their orientational relationships with respect to the host has been deduced from single crystal X-ray diffraction photographs recorded at room temperature. For OP/urea, UP/urea and LP/urea, the guest structure in the three-dimensionally ordered regions is monoclinic, and six types of domain of this monoclinic structure can be identified within each single crystal. The relative packing of diacyl peroxide molecules is the same in each domain, and the different domains are related by 60° rotation about the channel axis. For each of these inclusion compounds, the offset between the ‘heights’ of the guest molecules in adjacent channels is the same ( ca . 4.6 Å (4.6 x 10 -10 m)) within experimental error, suggesting that the relative interchannel packing of the guest molecules is controlled by a property of the diacyl peroxide group. In addition to revealing these novel structural properties, the work discussed in this paper has more general relevance concerning the measurement and interpretation of single crystal X-ray diffraction patterns that are based on more than one three-dimensionally periodic reciprocal lattice. Seven separate reciprocal lattices are required to rationalize the complete X-ray diffraction pattern from each diacyl peroxide/urea crystal studied here.

scholarly journals Reply to comment on Couzi et al . (2018): a phenomenological model for structural phase transitions in incommensurate alkane/urea inclusion compounds

2019 ◽  
Vol 6 (8) ◽  
pp. 190518 ◽  
Author(s):  
Kirsten Christensen ◽  
P. Andrew Williams ◽  
Rhian Patterson ◽  
Benjamin A. Palmer ◽  
Michel Couzi ◽  
...  
Keyword(s):  
Phase Ii ◽  
Phenomenological Model ◽  
Inclusion Compounds ◽  
Phase Iii ◽  
X Ray Diffraction ◽  
X Ray ◽  
Urea Inclusion Compounds ◽  
Full Support ◽  
Link Type ◽  
Urea Inclusion

In a recent paper (Couzi et al. 2018 R. Soc. open sci. 5 , 180058. ( doi:10.1098/rsos.180058 )), we proposed a new phenomenological model to account for the I↔II↔“III” phase sequence in incommensurate n -alkane/urea inclusion compounds, which represents an alternative interpretation to that proposed in work of Toudic et al. In a Comment (Toudic et al. 2019 R. Soc. open sci. 6 , 182073. ( doi:10.1098/rsos.182073 )), Toudic et al. have questioned our assignment of the superspace group of phase II of n -nonadecane/urea, which they have previously assigned, based on a (3 + 2)-dimensional superspace, as C222 1 (00 γ )(10 δ ). In this Reply, we present new results from a comprehensive synchrotron single-crystal X-ray diffraction study of n -nonadecane/urea, involving measurements as a detailed function of temperature across the I↔II↔“III” phase transition sequence. Our results demonstrate conclusively that “main reflections” ( h, k, l , 0) with h+k odd are observed in phase II of n -nonadecane/urea (including temperatures in phase II that are just below the transition from phase I to phase II), in full support of our assignment of the (3+1)-dimensional superspace group P2 1 2 1 2 1 (00 γ ) to phase II. As our phenomenological model is based on phase II and phase “III” of this incommensurate material having the same (3+1)-dimensional superspace group P2 1 2 1 2 1 (00 γ ), it follows that the new X-ray diffraction results are in full support of our phenomenological model.

Diffuse and satellite scattering in urea inclusion compounds with various alkane molecules

1996 ◽  
Vol 211 (4) ◽  
Author(s):  
Th. Weber ◽  
H. Boysen ◽  
M. Honal ◽  
F. Frey ◽  
R. B. Neder
Keyword(s):  
Inclusion Compounds ◽  
Diffuse Scattering ◽  
Room Temperature ◽  
Guest Molecules ◽  
X Ray ◽  
Urea Inclusion Compounds ◽  
Urea Inclusion

AbstractX-ray diffuse scattering phenomena and satellite reflections in urea inclusion compounds with guest molecules of varying lengths (tridecane, tetradecane, pentadecane, heptadecane and a mixture of pentadecane and hexadecane) were investigated between room temperature and 30 K. It was found that diffuse

Definitive Structural Characterization of the Conventional Low-Temperature Host Structure in Urea Inclusion Compounds

1997 ◽  
Vol 53 (5) ◽  
pp. 822-830 ◽  
Author(s):  
L. Yeo ◽  
K. D. M. Harris
Keyword(s):  
Low Temperature ◽  
Inclusion Compounds ◽  
Temperature Phase ◽  
Temperature Structure ◽  
Tunnel Structure ◽  
X Ray Diffraction ◽  
Guest Molecules ◽  
Urea Inclusion Compounds ◽  
Urea Inclusion ◽  
Low Temperature Phase

Structural properties of the 1,10-dibromodecane/urea and 1,12-dibromododecane/urea inclusion compounds have been determined by single-crystal X-ray diffraction for both the high- and low-temperature phases. In the high-temperature phase both inclusion compounds have the conventional hexagonal urea tunnel structure, with substantial orientational disorder of the guest molecules. In the low-temperature phase the urea tunnel structure distorts to an orthorhombic structure, based on a distorted form of the orthohexaganol cell of the high-temperature structure and with the loss of the C centre. Within this tunnel structure there is evidence that the guest molecules have a narrow distribution of orientations (with respect to rotation about the tunnel axis) and the preferred orientation of the guest molecules correlates well with the observed distortion of the host tunnel. This represents the first accurate and reliable report of the conventional low-temperature structure of urea inclusion compounds. Previous powder X-ray diffraction studies have confirmed that the host structure in the low-temperature phase of 1,10-dibromodecane/urea is the same as that in the low-temperature phase of the alkane/urea inclusion compounds.

UREA INCLUSION COMPOUNDS OF n-ALKYL BROMIDES AND IODIDES

1964 ◽  
Vol 42 (5) ◽  
pp. 1069-1072 ◽  
Author(s):  
Jack Radell ◽  
B. W. Brodman ◽  
E. D. Bergmann
Keyword(s):  
Powder Diffraction ◽  
Diffraction Data ◽  
Inclusion Compounds ◽  
Powder Diffraction Data ◽  
Cross Sectional ◽  
X Ray ◽  
Urea Inclusion Compounds ◽  
Alkyl Bromides ◽  
The Stability ◽  
Urea Inclusion

The formation and stability of urea inclusion compounds of n-alkyl bromides and iodides were established from X-ray powder diffraction data. The stability of both homologous families is greater than would be expected from a consideration of the cross-sectional diameter of the molecules only. The procedure for isolating the complexes has been simplified.

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