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.

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.

THERMAL DECOMPOSITION OF MOLECULAR COMPLEXES: IV. FURTHER STUDIES OF THE β-QUINOL CLATHRATES

1966 ◽  
Vol 44 (12) ◽  
pp. 1373-1385 ◽  
Author(s):  
H. G. McAdie
Keyword(s):  
Thermal Decomposition ◽  
Guest Molecule ◽  
Molecular Complexes ◽  
X Ray Diffraction ◽  
Interpenetrating Networks ◽  
Guest Molecules ◽  
X Ray ◽  
Guest Species ◽  
Decomposition Increase ◽  
Thermal Stability Of

The endothermal decomposition of 18 β-quinol clathrates has been studied by thermo-analysis, calorimetry, and X-ray diffraction, and the decomposition process shown to be[Formula: see text]For those symmetrical guest molecules (M) which do not distort the β-quinol cavities from their normal dimensions, both temperatures and enthalpies of clathrate decomposition increase with increasing volume of the guest molecule. For those unsymmetrical guest species which require distortion of the cavities along their c-axis, temperatures and enthalpies of decomposition tend to decrease as the initial distortion required to accommodate the guest increases. Thermal stability of β-quinol clathrates is thus strongly influenced both by the size and shape of the guest molecule.The mechanism of thermal decomposition is suggested to involve a combination of the loss of stabilizing guest–wall interactions, together with increased thermal motion of the interpenetrating networks of hydrogen-bonded quinol molecules.

Origins of thermodynamic stability of urea:alkane inclusion compounds

1998 ◽  
Vol 76 (11) ◽  
pp. 1695-1698 ◽  
Author(s):  
Mary Anne White
Keyword(s):  
Thermodynamic Stability ◽  
Inclusion Compounds ◽  
Solid Phase ◽  
Minor Role ◽  
Melting Points ◽  
Urea Inclusion Compounds ◽  
Guest Species ◽  
The Stability ◽  
A Minor ◽  
Urea Inclusion

Using existing thermodynamic data, the thermodynamic stabilities of urea inclusion compounds with three different alkane guests (decane, dodecane, and hexadecane) have been determined. In all cases the inclusion compounds are found to be thermodynamically stable with respect to their component species up to their melting points. From the present analysis, the solid-solid phase transitions are found to play only a minor role in stabilization, and the thermodynamic stability is found to be predominantly enthalpically driven. At a given temperature, the stability increases in the order urea:decane < urea:dodecane < urea:hexadecane. The present analysis shows that above the melting point of the guest species the inclusion compounds become much less stable because of the competition of the liquid guest. This destabilization eventually leads to incongruent melting.Key words: urea inclusion compounds, thermodynamic stability.

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.

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.

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