Lower Rim Calix(4)arene Ketone Derivatives and their Interactions with Alkali Metal Cations. Structural and Thermodynamic (Solution and Complexation) Characterization of the Tetraphenyl Ketone Derivative and its Sodium Complex

A. F. DANIL DE NAMOR; D. KOWALSKA; E. E. CASTELLANO; O. E. PIRO; F. J. SUEROS VELARDE; J. VILLANUEVA SALAS

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

Royal Society of Chemistry

Año: 2001 vol. 3 p. 4010 - 4021

1463-9076

A modiÐed method for the synthesis of 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetra(benzoyl)methoxycalix(4)arene (1) and 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetra(acetoyl)methoxycalix(4)arene (2) using 18-crown-6 as phase transfer catalyst is reported. Ligand 1 was structurally (1H NMR and X-ray crystallography) and thermodynamically characterised. An account of the steps required for the formulation of an equation representative of the complexation process involving metal cations and macrocycles is given using as an illustrative example the interaction of 1 with the Na(I) cation. Thus, detailed thermodynamics of this system are Ðrst reported taking into account the solution properties of the reactants and the product in various solvents with the aim of assessing quantitatively the medium e.ect on the complexation process. The sodium : monoacetonitrile : 1 complex was isolated and its molecular structure was determinated from X-ray di.raction data. The calix now adopts a more symmetric cone conformation than the free ligand and its hydrophobic cavity is Ðlled with an acetonitrile solvent molecule. The hydrophilic pocket hosts the sodium cation which is in an eight-fold coordination with the four ethereal oxygen atoms [average d(Na-O) = 2.45(4) A] and the four carbonyl oxygen atoms [average d(Na-O) = 2.51(4) A] forming the corners of a distorted Archimedean square antiprism. The key structural features relevant to the complexation process are discussed. 1H NMR and conductance measurements have been used to assess the interaction of 1 and 2 with alkali metal cations. Final conclusions are given. Attention is drawn about the relevance of detailed thermodynamic studies on cation complexation processes involving calixarene derivatives. This is discussed within the context of selectivity and the factors controlling it in solution processes.