Koilands centrosymmetric

Figure 8 Schematic representation of koilands (hollow molecular building blocks bearing two preorganised cavities oriented at a 180° angle) centrosymmetric koiland (a), noncen-trosymmetric koilands based on electronic differentiation (b and c), geometrical differentiation (d) and both electronic and geometrical differentiation (e). A and B represent calix[4]arene units and M, Mi and M2 atoms used to fuse two calix units.

Figure 15 A portion of the structure of koilates formed through self-inclusion by the centrosymmetric self-complementary koilands 14 (a) and 11 (b) and the interconnection of consecutive koilates by hexadiyne molecules 33 (c) (see text for more details). For the sake of clarity, hydrogen atoms are not represented.

In solution, as expected, 29Si NMR studies revealed the presence of two signals for all noncentrosymmetric heterodimers, whereas for the centrosymmetric koilands a unique signal was observed. 

For the geometrically differentiated noncentrosymmetric koiland 22 based on the double fusion of the p-tert-butyl calix 5 and p-allyl calix unit 6 by two Si atoms, the formation of directional koilates was studied using p-xylene 31 as a centrosymmetric (Figure 4g and h) and phenylpropyne 34 as a noncentrosymmetric (Figure 4f) connectors [81]. 

Figure 18 A portion of the X-ray structure of the koilate formed between the mono fused koiland 23 and hexadiyne 33 as connector. The directional 1-D network is obtained by a single translation in a noncentric fashion of two different assembling cores defined by the inclusion of the connector into the two differentiated cavities of the koiland (a) and a portion of the structure showing the centrosymmetric packing of consecutive directional koilates leading to a nonpolar solid (b). For the sake of clarity, the carbon atoms of the connector are coloured in grey and the hydrogen atoms are not represented.

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