Thioureas channel-type

Figure 6. (b) The channel-type structure of inclusion compounds of thiourea viewed along the c axis. For clarity the guest molecules are represented by large circles. (Data from ref. 36b). 

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. 

Basically, there are two main classes of urea/thiourea inclusion compounds the classical channel-type clathrates having a host lattice constructed from urea (Figure 8.1) or thiourea molecules (Figure 8.2) [1] and those whose host lattices contain anions as... 

Figure 8.35 Perspective view of the crystal structure of [(C2H5)4lsP]2C404 6(NH2)2CS (17) showing individual columns of well-ordered tetraethylammonium cations enclosed in the channel-type host lattice built of squarate-thiourea species. The origin of the unit cell lies at the upper left corner, with a pointing towards the reader, b downward and c from left...

The most prominent structural feature of these three channel-type inclusion complexes is their analogous linkage mode of thiourea molecules which leads to the same type of... 

Another type of inclusion compd is the channel or canal compound. Here the straight chain compds, such as hydrocarbons, acids,esters , alcohols, aldehydes, ketones, etc are enclosed in the channels formed by compds, such as urea, thiourea, choleic acids, cyclodextrins, etc. As examples of channel compds may be cited, the urea-decone compd, [CO(NH2)2] g.C, 2H26, and various zeolites. (See also Ref 10, pp431 ... 

Qathrate compounds are of this type molecules of one substance are trapped in the open structure of molecules of another. Hydroquinone forms clathrate compounds with SO2 and methanol, for example. Urea and thiourea also have the property of forming complexes, known as adducts, with certain types of hydrocarbons. In these cases molecules of the hydrocarbons fit into holes or channels in the crystals of urea or thiourea the shape and size of the molecules determine whether they will be adducted or not. 

Vinyl monomers included in channels in compounds such as urea [24], thiourea [25], perhydrotriphenylene [26], desoxycholic acid [27], and so on, are polymerizable. In these reactions the walls of the channel provide the control which leads to stereoregularity of the polymers formed. The second type of system consists of cyclic monomers, such as trioxan, which polymerize by a process involving opening of the monomer ring followed by coupling with neighbors [12]. 

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