Molecular model for host–guest interaction of tetraamino-tert-butylthiacalix[4]arene and tetraamino-tert-butylcalix[4]arene receptors with carboxylate and dicarboxylate guests: an ONIOM study.

Geometry optimizations of tetraamino-tert-butylthiacalix[4]arene (tatbtc4a) and tetraamino-tert-butylcalix[4]arene (tatbc4a) complexes with acetate, oxalate,malonate, succinate, glutarate, adipate, and pimelate were carried out using the integrated MO:MO method. Thermodynamic quantities, preorganization energies and complexation energies of these complexes were obtained at the ONIOM(B3LYP/6-31G(d):AM1) level of theory. The relative stabilities of the tatbtc4a and tatbc4a complexes with carboxylate guests are reported. The complexes tatbtc4a/malonate and tatbc4a/oxalate were found to be the most stable species. The selectivity of the tatbtc4a receptor toward to malonate with respect to oxalate, in terms of selectivity coefficient, K(oxalatemalonate) is 9.90×10(2).