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

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-Ahexakis(N,N-diaethylaminocarbonyl)methoxycalix[6] arene)(I) in a binary mixture of deuterated chloroform and acetonitrile was studied by 1H, A133Cs NMR spectroscopy and X-ray crystallography. Different complexes between Cs+ and I with Cs+:I stoichiometries ranging from 1 to 3 are Aformed 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 Ais similar to the distorted partial cone crystal structure in the solid state. The two caesium cations are coordinated to carbonyl and phenolic Aoxygens, with a short distance of 4.16 A between them. The dissociation of the 2 :1 complex follows a dissociative mechanism with (delta)H<>= A58 kJ mol–1 and (delta)S<>=–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 Auncomplexed calix[6]arene hexaacetamide.