Packing inclusion crystals

FIGURE 26. Molecular packing of the inclusion crystal of 209 and argon at 103 K. Positions of Ar atoms are marked by circles. Projection down the c axis. Reproduced by permission of VCH VerlagsgesellschaftmbH from Reference 322... 

Figure 11 Packing coefficients in various states organic crystals, protein cores, inclusion crystals, encapsulated hosts and the liquid state.

By Methods A and B, isopropyl phenyl sulfoxide was included in crystalline 1 with high ( -enantioselectivity (86 and 87% ee, respectively). Ethyl phenyl sulfoxide formed no inclusion compound by Method A, but the inclusion compound of its (5)-enantiomer was obtained by Method B. The inclusion crystal of (.V)-e(hyl phenyl sulfoxide is isostructural with that of (S)-isopropyl phenyl sulfoxide (Figure 3). As mentioned above, (6>ethyl phenyl sulfoxide was not included by Method A. The lack of one methyl group may make enthalpy (interaction with the inclusion cavity) and entropy disadvantageous in crystal packing to result in no inclusion of ethyl phenyl sulfoxide via Method A. 

Figure 10 Molecular structure of 2a and crystal packing of (a) the chiral inclusion crystal 2a (- )4 and (b) the chiral crystal of 2a on its own. (c) Space-filling representation of molecular structure of 2a as found in the two crystal structures. Conformations are similar in the two cases.

Figure 26.3 Representative packing diagrams for inclusion crystals ofcholic acid and its derivatives. The crystals exhibit guest-responsive structures.

Nakano, K., Sada, K., Kurozumi, Y. and Miyata, M. (2001) Importance of packing coefficients of host cavities in the isomerization of open host frameworks guest-size-dependent isomerization in cholic acid inclusion crystals with monosubstituted benzenes. 

Fig. 10. Constitutions of brucine (22) and sparteine (23) which are useful for enantioselective inclusion crystallization. The diagram shows the crystal packing of a corresponding clathrate of 22 [guest molecule being 3-(2-bromophenyl)-3-phenyl-l-propyne-3-ol, and is shaded] ...

A racemic inclusion crystal is also obtained when the guest molecule is other than chloroform. 1 forms a similar 1 1 molecular cavity inclusion complex with methylene chloride, but in a different space group C2/c (Table III). In marked contrast to the type I crystal, the heterocyclophane in the CH Clo complex takes both "R"- and "S"-confor-mations (Type II, racemic inclusion crystal). A schematic picture of the host-guest packing in the methylene chloride complex is shown in Fig 2. 

Packing of the cyclodexthn molecules (a, P, P) within the crystal lattice of iaclusion compounds (58,59) occurs in one of two modes, described as cage and channel stmctures (Fig. 7). In channel-type inclusions, cyclodextrin molecules are stacked on top of one another like coins in a roU producing endless channels in which guest molecules are embedded (Fig. 7a). In crystal stmctures of the cage type, the cavity of one cyclodextrin molecule is blocked off on both sides by neighboring cyclodextrin molecules packed crosswise in herringbone fashion (Fig. 7b), or in a motif reminiscent of bricks in a wall (Fig. 7c). 

The inclusion of both covalent and intermetallic crystals in Chapter 6 is predicated on the close relation between the covalent and metallic bonds, as discussed in Chapter 3. SP 54 and SP 55 are beautiful examples of the complexity of the atomic packing and bonding arrangements in alloy structures, which fascinated Pauling. 

On the other hand, the crystallization process of diolefin compounds often plays a significant role in determining their topochemical behaviour, by changing their crystal structure or by forming solvent inclusion complexes. Furthermore, topochemical photoreactions of crystals with )8-type packing are accompanied by thermal processes under moderate control by the reacting crystal lattice (see p. 140). These factors seriously complicate the whole reaction scheme. 

Fig. 3. Channel inclusion compound of deoxycholic acid (6) with acetone. The crystal packing is affected by head-to-tail H-bond-mediated double layers of host molecules (H-bonds as dotted lines, guest molecules shaded) (Adapted from Ref. 13)...

The hydrocarbons 54 and 5551) which are functional group-free analogues of 26 and 38 display no activities of inclusion formation, either with polar or with apolar solvents371. This result is another proof that mostly for the roof-shaped type of compounds, functional groups play a fundamental role in the construction of a low-density packed crystal lattice. 

Table 11. Crystal data and packing coefficients for the alcohol inclusions of 1...

Enantioselective photocyclization of 74 occurred efficiently in the inclusion complex with 2a. In particular, the selectivity is very high in the case of 74a. However, control is inefficient in the 1 2 complex 85 composed of 2a and 74c. The host guest ratio probably depends on the packing of the components in the crystal. The packing is... 

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