Complexation of the caesium cation by the host p-tert-butylcalix[6]arene hexaacetamide

摘要

The complexation of the caesium cation by a p-tert-butylcalix[6]arene hexaacetamide derivative (5,11,17,23,29,35-hexa-tert-butyl-37,38,39,40-hexakis(N,N-diaethylaminocarbonyl)methoxycalix[6]arene) (I) in a binary mixture of deuterated chloroform and acetonitrile was studied by ~1H, ~(133)Cs NMR spectroscopy and X-ray crystallography. Different complexes between Cs~+ and I with Cs~+:I stoichiometries ranging from 1 to 3 are formed in solution. The 3:1 complex is only observed below 250 K, in the presence of excess of Cs~+. The structure of the 2:1 complex in solution is similar to the distorted partial cone crystal structure in the solid state. The two caesium cations are coordinated to carbonyl and phenolic oxygens, with a short distance of 4.16 A between them. The dissociation of the 2:1 complex follows a dissociative mechanism with ΔH~≠ = 58 kJ mol~(-1) and ΔS~≠ = -2 J K~(-1) mol~(-1). The activation parameters indicate that the dissociative process is kinetically governed by the successive flipping of two aromatic rings leading to a 1,2,3 alternate conformation of a 1:1 complex, similar to the crystal structure of the uncomplexed calix[6]arene hexaacetamide.