Abstract
Novel self-filled azacalixarenes were synthesized following a simple method. The structure of a p-xylylene-bridged compound was investigated by X-ray crystallographic analysis. Compound 1: C42H44 O4N2, monoclinic, space group C2/c, a = 17.236 (4), b = 9.244 (3), c = 22.217 (4) Å, β = 101.23 (1)°, D calc 1.226 g/cm3, V=3472 (1)Å3,Z=4,R = 0.042. The final cycle of full-matrix least-squares refinement was based on 2201 observed reflections [I>3.00[sgrave](I)] and 284 variable parameters. Dynamic NMR and MM3 calculations were also employed to study the structures in solution. Azacalix[4] skeletons are rigidly fixed in shallow cone conformations and bridging xylylene units (p- and m-) are located in the cavities of the cyclic skeletons. Intra-cavity hydrogen bonds between OH and N atoms localize at low temperatures. The free energy of the localization was estimated to be 10.8 and 11.2 kcal mol−1 for p- and m-xylylene-bridged compounds, respectively.
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