Conformationally Flexible p-Sulfonated Calix[5]arene Binding with Large Bis-Phosphonium Cations

Water-soluble p-sulfonated calix[5]arene forms a multicomponent complex with aquated Gd(III) ions and bis-phosphonium cations, where the calixarenes are arranged in bilayers with the bis-phosphonium cations embedded between and within the bilayers. The calixarenes are significantly distorted from the common "cone" conformation and are linked from one bilayer to another through the sulfonate groups via secondary coordination sphere interactions associated with homoleptic aquated metal ions.