Thiourea inclusion complexes

Thiourea inclusion complexes. As noted in the second paragraph beginning on 1, 1165, a Delft group (Verkade et al.s) reported an efficient separation of cis-and trarcs-4-isopropylcyclohexane-l-carboxylic acid based on their observation that the trans-acid forms a thiourea inclusion complex whereas the cis isomer does not. However, they failed to account for the difference. A simple explanation became... 

Inclusion complexes. The explanation which we presented (2, 412-413) for the formation of a thiourea inclusion complex from trcarboxylic acid but not from the c/s-isomer is invalidated by the further finding of the Delft group1 that the methyl esters of these two acids both form thiourea inclusion complexes. 

Anderson, A.G. Calabrese, J.C. Tam. W. Williams, I.D. Thiourea inclusion complexes of organometallics Optically non-linear materials. Chem. Phys. Lett. 1987, 134. 392. 

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. 

Host — A - molecular entity that forms an -> inclusion complex with organic or inorganic -> guests, or a - chemical species that can accommodate guests within cavities of its crystal structure. Examples include cryptands and crowns (where there are -> ion-dipole interactions between heteroatoms and positive ions), hydrogen-bonded molecules that form clathrates (e.g., hydroquinone and water), and host molecules of inclusion compounds (e.g., urea or thiourea). The - van der Waals forces and hydrophobic interactions (- hydrophobic effect) bind the guest to the host molecule in clathrates and inclusion compounds. 

Figure 18 (a) Sketch of the thiourea/dimethylbutadiene-inclusion complex structure and electron density map of the cross-section of the... 

The work reported here has shown that inclusion complexation of organic and organometallic chromophores by thiourea, TOT and cyclodextrins can induce second harmonic generation capability in the polar crystals which result, even when the original bulk materials are themselves incapable of SHG. Structural evidence has been presented to show tht the solid state inclusion structures are acentric, and a simple electronic picture t0 the polarization response of these materials within the two-state modeP ° has been discussed. In an earlier section we remarked that of the many complexes we have made, only one has NOT been acentric. This result was not anticipated. We postulate that it is a natural tendancy in such materials, rather that an exception. If we consider a dipolar molecule in isotropic solution, we can imagine that if it were to aggregate, it would do so in a head to tail fashion in order to minimize electrostatic repulsion. The situation is illustrated in Scheme 3. The arrangement that would result is centrosymmetric. 

To work up the mother liquor from the crystallization from methanol, first evaporate the solvent. Note that the residual oil does not solidify on ice cooling. Next, dissolve the oil, together with 5 g of thiourea, in 50 mL of methanol, collect the inclusion complex that crystallizes (3.2 g), and recover 1,4-di-/-butylbenzene from the complex as before (0.8 g before crystallization). 

There are of course more organic compounds which can be used as host molecules in the formation of inclusion complexes. For most of them, e.g. urea and thiourea, crown ethers, cholic acid, hydroquinone, tri-o-thymotides and Di-anin s compound, the literature describing SS NMR applications in structural... 

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). 

Preparation B. Ault and Kopet2 describe as an introductory organic experiment a procedure for the preparation of adamantane by isomerization of endo-tetrahydrodicyclopentadiene by the method of Schleyer but the product is isolated from a hexane extract of the reaction mixture as the beautifully crystalline inclusion complex with thiourea.3 As noted in 1, 1164, the ratio in this complex is 3.4 molecules of host per molecule of guest hydrocarbon. Although the reaction time is only 1 hour, the yield (15%) is about the same as that reported for a reaction time of 8-12 hours. 

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. 

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. 

Inclusion complexes of a variety of (77 -ligand)M(CO)3 compounds including (77 -thiophene)Cr(CO)3 and CpM(CO)3 (M = Mn, Re) with thiourea have been tested using powder SHG, but all showed SHG efficiencies lower than that of urea.l The cymantrenyl group has also been incorporated into donor-acceptor compounds some examples studied by HRS (1064 nm) are shown in Figure Moving from 68 to 69 to 70 or from 71 to 72 to 73 shows an... 

Complexes of various donor-substituted alkynes, such as FcCH=CHC CPh with WTp COI Fc = ferrocenyl Tp" = hydridotris(3,5-dimethylpyrazolyl)borate, have been studied using powder SHG at 1,064 nm, but efficiencies were considerably less than that of urea the molecular NLO properties have not been studied. The isomers of (dppe)( 7 -C6o)M(CO)3 (M = Cr, Mo) show complex 2-scan (532, ns pulses) behavior which is not only due to electronic effects, but also due to excited-state processes. The inclusion complexes formed by several ( -ligand)Fe(CO)4 species with thiourea were subjected to the Kurtz-Perry powder technique, but none exceeded... 

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. 

Matsuo, T. Sekii, M. Suga, H. Nakamura. N. Cl NQR study of guest dynamics in thiourea-CC inclusion complex. Z. Naturforsch. 1990, 45a. 519-522. 

Gopal, R. Robertson. B.E. Rutherford, J.S. Adamantane inclusion complexes with thiourea and selenourea. Acta Crystallogr. 1989. C45. 257. 

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... 

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