Core modified meso-aryl sapphyrins and rubyrins: structural and anion receptor properties

Studies on structural characterisation and anion binding properties of a se ries of core modified meso-aryl sapphyrins and rubyrins are described. It h as been shown that the sapphyrins and rubyrins bind anions such as F-, N-3( -) and CO32- in their protonated form. The binding constants evaluated for a particular sapphyrin vary in the order F- congruent to N-3(-)< CO32- and this has been accounted for in terms of compatibility of the cavity size of the sapphyrin, the anion size and the complete charge neutralisation. Howe ver, for the protonated rubyrins, this order is reversed because of the lar ger cavity sizes of the rubyrins relative to the sapphyrins. A comparison o f the magnitude of binding constants with those of beta-substituted N5 sapp hyrins indicates a decrease of several orders of magnitude because of the a vailability of fewer hydrogen bonding sites for the core modified meso-aryl sapphyrins reported here. Furthermore, the single crystal X-ray structures of two sapphyrins reveal the inversion of the heterocyclic ring opposite t o the bithiophene/biselenophene unit, while the rubyrins show planar struct ures.