p-tert-Butylcalix[6]arene hexacarboxylic acid conformational switching and octahedral coordination with Pb(ii) and Sr(ii)

Abstract

p-tert-Butylcalix[6]arene hexaacetic acid is in a symmetric cone conformation in CHCl₃, but it becomes conformationally flexible in CHCl₃/CH₃CN (1 : 1). In this mixture the host has a strong binding affinity towards Pb(II) and instantly forms a complex of low symmetry – shortly thereafter structural reorganization occurs resulting in a high symmetry complex of Pb(II) in an octahedral cage of carboxylates. Sr(II) and Ba(II) display similar behavior over a longer period of time.