Anions in supramolecular chemistry : binding, sensing and assembly

This thesis deals with the synthesis and study of the anion complexation properties of new organic anion receptors. Firstly a series of pyrrole amide cleft receptors has been produced in order to investigate whether such simple molecules may behave as efficient anion coordinating agents. Indeed, high selectivity for oxoanions such as benzoate and amide clefts combining electron withdrawing groups at the 3- and 4- position of the pyrrole or directly appended at the amide positions has also been achieved. The aim of this project was to discover whether enhancing the acidity of the pyrrole NH or the amide NH groups via the introduction of chloro- or nitro- groups in the receptor skeleton could result in an enhanced interaction strength of the resulting receptor/anion complex. Not only was this target achieved, additionally the new electron withdrawing functionalized pyrroles clefts revealed unexpected properties such as the ability to form novel anionic dimers in the solid state and to selectively sense fluoride anions via a colorimetric response. New 'super-extended' cavity calix[4]pyrroles have also been synthesised and the anion coordination properties of these receptors studied. These new compounds were found to bind fluoride anions exclusively in DMSO solution. The preference for fluoride was found to be so evident that these receptors were able to detect half of one equivalent of fluoride anions even in the presence of 100 equivalents of other undetected anions such as chloride, bromide, iodide, hydrogensulfate and hydrogenphosphate. The high selectivity for fluoride has been rationalized by molecular modelling studies carried out in collaboration with Dr. J. W. Essex at the University of Southampton.