Conformation double partial cone

The conformations of the parent calix[6]arenes have been variously described as distorted cone [6 - ], double partial cone and 6 ° winged... 

Extending the macrocycle ring to six-membered ring fives more flexibility to the calix[6]arene molecule compared to three- four- and five-membered calixarenes. For calix[6]arenes eight main (basic) conformations are defined [41] distorted cone, compressed cone, pinched cone, double partial cone, winged, 1,2,3-altemate, 1,3,5-altemate and distorted 1,2,3-altemate. Other conformations are also observed... 

There is only eight crystal structures of calix[7]arenes deposited in CSD. The reason for this is much more difficult synthesis of seven-membered calixarenes and/or difficulties in obtaining monocrystals of this compounds and their complexes/co-crystals. Like for smaller calixarenes discussed above also here the self-inclusion of one of the substituent may occur like in para-t-hvXy -carboxymethoxycalix[7]arene/deuterochloroform clathrate (Fig. 38.25a) [52] or inclusion complexes are obtained. For the later, due to a great degree of flexibility, many conformations of calixarene host molecule is possible but the most observed is a double partial cone, e.g. 1 2 para-t-butyl-calix[7]arene/pyridine inclusion complex where one guest molecule is located in each partial cone cavity (Fig. 38.25b) [53]. In one case the flattened cone conformation was found where the (Fig. 38.25c). In this crystal structure one toluene and one disordered benzene/ toluene molecule are involved in inclusion complex formation with one para-t-butyl-calix[7]arene molecule [54]. 

Calix[6]arenes in partial double cone and inverted partial double cone conformation may adopt in each pseudocalix[4]arene a guest molecule [49]. But it is also observed that the guest molecule is located in one cavity while the second one is occupied by a one of the substituents of neighboring calixarene, similarly to inclusion dimer formation in calix[4]- and calix[5]arenes. The examples are shown in Fig. 38.23. 

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