New bis- and tris-ferrocenoyl and tris-benzoyl lower-rim substituted calix[5]arene esters: Synthesis, electrochemistry and X-ray crystal structures

New tris-benzoyl-, tris-ferrocenoyl- and bis-ferrocenoyl p-tert-butylcalix[5]arene esters have been synthesised (1-3 respectively) by reaction of the parent calixarene with the appropriate acid chloride. X-ray crystal structures of all three compounds have been determined with the structure of 2 revealing an ethanol guest molecule bound deep in the cavity of the calix[5]arene. The electrochemical properties of 2 have been extensively investigated using rotating disk electrode, cyclic and square wave voltammetric techniques. Electrochemical evidence is presented suggesting 2 has the capability of detecting neutral polar guest molecules, such as dimethylformamide, in dichloromethane solutions.