Structural properties of α,ω-dibromoalkane/urea inclusion compounds: a new type of interchannel guest molecule ordering

1991 ◽  
Vol 87 (20) ◽  
pp. 3423-3429 ◽  
Author(s):  
Kenneth D. M. Harris ◽  
Sharon P. Smart ◽  
Mark D. Hollingsworth
Keyword(s):  
Structural Properties ◽  
Inclusion Compounds ◽  
Guest Molecule ◽  
Urea Inclusion Compounds ◽  
New Type ◽  
Urea Inclusion

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 A phenomenological model for structural phase transitions in incommensurate alkane/urea inclusion compounds

2018 ◽  
Vol 5 (6) ◽  
pp. 180058 ◽  
Author(s):  
Michel Couzi ◽  
François Guillaume ◽  
Kenneth D. M. Harris
Keyword(s):  
Structural Properties ◽  
Phenomenological Model ◽  
Inclusion Compounds ◽  
Structural Phase ◽  
Temperature Phase ◽  
Coupling Mechanism ◽  
Repeat Distance ◽  
Guest Molecules ◽  
Urea Inclusion Compounds ◽  
Urea Inclusion

n -Alkane/urea inclusion compounds are crystalline materials in which n -alkane ‘guest’ molecules are located within parallel one-dimensional ‘host’ tunnels formed by a helical hydrogen-bonded arrangement of urea molecules. The periodic repeat distance of the guest molecules along the host tunnels is incommensurate with the periodic repeat distance of the host substructure. The structural properties of the high-temperature phase of these materials (phase I), which exist at ambient temperature, are described by a (3 + 1)-dimensional superspace. Recent publications have suggested that, in the prototypical incommensurate composite systems, n -nonadecane/urea and n -hexadecane/urea, two low-temperature phases II and ‘III’ exist and that one or both of these phases are described by a (3 + 2)-dimensional superspace. We present a phenomenological model based on symmetry considerations and developed in the frame of a pseudo-spin–phonon coupling mechanism, which accounts for the mechanisms responsible for the I ↔ II ↔ ‘III’ phase sequence. With reference to published experimental data, we demonstrate that, in all phases of these incommensurate materials, the structural properties are described by (3 + 1)-dimensional superspace groups. Around the temperature of the II ↔ ‘III’ transition, the macroscopic properties of the material are not actually associated with a phase transition, but instead represent a ‘crossover’ between two regimes involving different couplings between relevant order parameters.

scholarly journals The changeable nature of urea inclusion compounds.

2014 ◽  
Vol 70 (a1) ◽  
pp. C1706-C1706
Author(s):  
Rachael Lee ◽  
Michael Probert ◽  
Jonathon Steed
Keyword(s):  
Inclusion Compounds ◽  
Guest Molecule ◽  
Domain Switching ◽  
Structural Features ◽  
Honeycomb Structure ◽  
Guest Molecules ◽  
Urea Inclusion Compounds ◽  
Β Phase ◽  
Diffraction Patterns ◽  
Urea Inclusion

Urea inclusion compounds (UICs), the β-phase of urea, have been known only since 1949 and have revealed various structural and behavioural characteristics of interest, largely influenced by the type of guest molecule present in the crystal. These structures have a hexagonally symmetrical honeycomb structure of a hydrogen-bonded urea network encapsulating the guest molecules, a defining motif of these clathrates. The simplest of this class contains an alkane guest (C7-C20), creating an incommensurate relationship between host and guest and a significantly disordered crystal structure with respect to the guest. As a result, diffuse scattering is typical in the diffraction patterns of UICs. As the guest molecules are altered, so too is the behaviour of the host network. With certain dihaloalkanes for example, the guest may coil into an atypical conformation in order to present a commensurate relationship with the host. This increase in guest order creates a distortion of the host network away from hexagonal symmetry, creating an internal stress which causes domain switching within the system. A number of different effects such as this can be seen on changing the guest molecule, ferroelasticity being an example for certain diketone guests. In this work we are exploring examples of UICs which, due to unusual interaction between the host and guest, display atypical structural features, symmetry or behaviour. These crystal structures are under investigation at a range of temperatures and pressures, by both X-ray and neutron diffraction techniques in order to fully understand the nature and bonding of UICs.

A New Type of Layered Structure for Urea Inclusion Compounds Containing Local Segments of Tunnels

2001 ◽  
Vol 123 (50) ◽  
pp. 12684-12685 ◽  
Author(s):  
Sang-Ok Lee ◽  
Benson M. Kariuki ◽  
Angela L. Richardson ◽  
Kenneth D. M. Harris
Keyword(s):  
Layered Structure ◽  
Inclusion Compounds ◽  
Urea Inclusion Compounds ◽  
New Type ◽  
Urea Inclusion

scholarly journals THERMAL DECOMPOSITION OF MOLECULAR COMPLEXES: III. UREA INCLUSION COMPOUNDS OF MONOSUBSTITUTED ALIPHATIC SERIES

1963 ◽  
Vol 41 (9) ◽  
pp. 2144-2153 ◽  
Author(s):  
H. G. McAdie
Keyword(s):  
Thermal Decomposition ◽  
Inclusion Compounds ◽  
Guest Molecule ◽  
Molecular Complexes ◽  
Decomposition Temperature ◽  
Urea Inclusion Compounds ◽  
Guest Species ◽  
Alkyl Bromides ◽  
Sufficient Energy ◽  
Urea Inclusion

Examination of the thermal decomposition of urea inclusion compounds has been extended to complexes of the even-numbered members of the following aliphatic series: n-alcohols, n-alkylamines, n-alkyl bromides, and n-carboxylic acids. The decomposition has been studied primarily by differential thermal analysis and an attempt made to correlate the observed decomposition temperatures and heats of decomposition with the particular guest species. The decomposition mechanism appears to involve acquisition of sufficient energy by the guest molecule to permit its diffusion from the canal, the decomposition temperature being related to the activation energy required for this diffusion process.

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