Inclusion compounds thiourea

Description of the Canal Structures of Urea and Thiourea Inclusion Compounds... 

Metallocenes (but only with unsubstituted cyclopentadienyl rings) also form thiourea inclusion compounds. X-ray diffraction and Mdssbauer data on the ferrocene inclusion compound show that at 295 K the guest molecules are orientationally disordered at the sites of 32 symmetry. A phase change at 162 K generates a more ordered structure78). 

Esr 79-811 and 13C MAS nmr methods 821 have also been used in the study of the thiourea inclusion compounds in addition to the techniques already described in detail. 

Size and conformational effects such as those described above have been exploited in a wide range of separation procedures. In a patented method for the separation of cis- and tranj-l-methyl-4-uohexylcyclohexane carboxylic acids only the tram isomer forms a thiourea inclusion compound 831. In solution the cis isomer always has an axial, equatorial arrangement in the chair conformation, while the trans isomer can exist as the diequatorial or diaxial chair conformers. It is not reported which of these is favoured or how the guest packs in the canals. 

Thiourea inclusion compounds have also found recent applications as diverse as the separation of liquid crystal isomers 84 ), isolation of petroleum constituents 85,86), and the recovery of squalene during olive oil refining87), to cite just a few examples. 

Thiourea inclusion compounds, 14 112 Thioureas, in polychloroprene curing, 19 848... 

Pedersen (1971) reported on a number of crystalline complexes with thiourea and similar molecules and found that the solubility of dibenzo-18-crown-6 [11] in methanol is enhanced by urea and thiourea. The latter observation precludes the possibility of the solid complexes being urea or thiourea inclusion compounds. Factors that are of importance in the complex formation are ring size (dibenzo-12-crown-4 did not form complexes), and steric hindrance in the complex caused by the guest molecule. Thiourea, N-phenylthiourea, and 2-thiazolidinethione form complexes but N,N,N -trimethylurea, thiocarbanilide and N-methylthiazolidinethione do not. 

The conformational properties of mono-substituted cyclohexanes, C V, 1111X, in their thiourea inclusion compounds have been studied102. Variable-temperature MAS spectra demonstrate that a chair-chair ring inversion process occurs in the thiourea tunnel, in which the axial and equatorial conformers are interconverted. Predominance of the equatorial conformer is found when X = NH2. 

For a review of urea and thiourea inclusion compounds, sec Takemolo Sonoda. in Atwood Davies MacNicol, Ref. 60. vol. 2, pp. 47-67. 

It has long been known that highly crystalline forms of polybutadiene with melting points higher than conventional crystalline polybutadiene are available via radiation polymerization of thiourea inclusion compounds (1. Crystallographic studies of the polymerization of butadiene derivatives in inclusion complexes have been reported (53). Recently, butadiene derivatives in layer perovskite salts have been polymerized to singlecrystal polymers which have been structurally characterized (54). 

The dicyclohexylamine/thiourea inclusion compound has been studied by CPMAS NMR. The results have shown that the guest (dicyclo-hexylamine) molecules are freely rotating and that the channels are perfect van der Waals cavities. 

Fig. 18. Schematic of the cyclohexane/thiourea-inclusion compound. The strain e and the order-disorder pseudospin variables extracted from NMR experiments were interpreted in the framework of Landau theory for phase transition I -> II.

Harris, K. D. M., Fundamental and applied aspects of urea and thiourea inclusion compounds , Supramol. Chem. 2007,19,47-53. 

Thiourea also forms inclusion-compounds. The presence of a sulphur atom instead of an oxygen atom in thiourea accounts for an increase in the size of the thriourea molecule and of the crystalline structure as a whole so that the central channel has a diameter of about 6.5A, Branched-chain hydrocarbons become trapped in the channel to form complexes. Thus 2, 2, 4-trimethyl pentane fits into the channel and yields thiourea inclusion-compound. Normal hydrocarbons do not fill the available space to an extent sufficient for stability and do not form complexes. 

The purpose of this review is to assemble and assess currently available information about structural modification of urea/thiourea inclusion compounds. We concentrate here on the structural aspects of new inclusion compounds with urea/thiourea/selenourea-anion host lattices, most of which were prepared and structurally analyzed in our laboratory. The versatility of urea or thiourea as a key component in the construction of novel anionic host lattices is clearly demonstrated by occurrence of many new types of linkage modes. The results show that co-molecular aggregates of urea or thiourea with other neutral molecules or anionic moieties can be considered as fundamental building blocks for the constructions of various types of novel host lattices. Comments on structure-property relationship for these inclusion compounds are made wherever appropriate. 

The chemistiy of urea and thiourea inclusion compounds has received much attention and is still a subject of continuing interest since their accidental discovery in 1940 [54 and 1947 [55], respectively. 

There are more striking differences in the unit-cell dimensions of the selenourea inclusion compounds than are observed for the thiourea inclusion compounds, as adaptation of the selenourea lattice to the shape and size of the included molecules is apparently relatively easy [57-Si]. A theoretical study of the conformations and vibrational frequencies in urea, thiourea, and selenourea compounds has been reported [54]. Studies on the complexation of TT with I" and urea, thiourea, or selenourea (and their Me derivetives) using a horizontal zone electromigration method have indicated that the complexing capacities of the urea derivatives increase in the order urea < thiourea < iV,N, N -tetramethylthiourea < selenourea [55]. 

We now present results illustrating that the N-H- 0 and N-H -S hydrogen bonds play an instrumental role in the structures of a novel class of urea/thiourea inclusion compounds. The average lengths of 84 measured N-H - O hydrogen bonds in 16 urea-anion inclusion complexes and 114 measured N-H—S hydrogen bonds in 23 thiourea-anion host lattices are listed in Table 11. 

Several IR and Raman spectroscopy studies of the thiourea inclusion compounds of monohalocyclohexanes have been reported The predominance of axial conformers in the cavities has been demonstrated, in contrast with the preferred equatorial conformation in the liquid or gaseous phases. No X-ray structures of the thourea complexes have been reported. 

Harris. K.D.M. Meldola lecture Understanding the properties of urea and thiourea inclusion compounds. Chem. Soc. Rev. 1997. 26. 279-289. 

Thiourea forms channel-type inclusion compounds with globular molecules.This is partly because the space group E3c lacks a screw axis that the space group of the urea inclusion compounds P6i22 possesses. The larger diameter of the channel than in the urea compounds accommodates cyclohexane and monosubstituted cyclohexane as well as carbon tetrachloride and hexachloro-ethane in the channel. With these more or less spherical molecules as the guest species, thiourea inclusion compounds are rich in their polymorphism, most undergoing two or more phase transitions below room temperature. 

Incommensurate and Commensurate Structures, p. 772 Inelastic Neutron Scattering, p. 727 Nuclear Magnetic Resonance Spectroscopy, p. 981 Nuclear Quadrupole Resonance Spectroscopy, p. 989 Thiourea Inclusion Compounds, p. 1501 Urea Inclusion Compounds, p. 1538... 

Desmedt, A. Kitchin, S.J. Guillaume, S. Couzi, M. Harris, K.D.M. Bocanegra, E.H. Phase transitions and molecular dynamics in the cyclohexane/thiourea inclusion compound. Phys. Rev. 2001, B64, 054106. 

Desmedt, A. Guillaume, F. Combet, J. Dianoux, A.J. A high resolution quasielastic neutron scattering study of the guest molecules dynamics in the cyclohexane/thiourea inclusion compound. Physica 2001, B301, 59. 

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