Conformational structures, proton affinity of p-tert-butylthiacalix[4]arene and its zinc complex

The conformational optimizations were performed on p-tert-butylthiacalix[4]arene and thiacalix[4]arene using the potential energy scan and semi-empirical AMI methods. The relative energies for all conformations were obtained with the HF/6-31G*//AM1 and B3LYP/631G*//AM1 methods. The relative stabilities of the most stable conformation of p-tert-butylthiacalix[4]arene conformers are in the following order: cone>partial cone>1,2-altemate>1,3-alternate. The energy difference between the two most stable conformers of p-tertbutylthiacalix[4]arene (cone 0000-AAAA and partial cone 0001-AAAA) is 9.05 kcal/mol. The reaction energies of proton affinity, deprotonation, preorganization of p-tert-butylthiacalix[4]arene cone conformer and complexation of its zinc complex were obtained with the B3LYP/6-31G* calculations. Both AMI and B3LYP/6-31G* optimized geometries of p-tert-butylthiacalix[4]arene cone conformer show good agreement with the X-ray crystallographic data. Electrostatic potential surfaces for LH4, LH3- and LH22- species of p-tert-butylthiacalix[4]arene (LH4) cone conformer are reported. (C) 2004 Elsevier B.V. All rights reserved.