Basicity investigation and structure optimization of polyaza-Calixarenes and stabilities of their complexes with metal cations

Abstract

The structure of 25, 26, 27, 28-tetra(2-ethoxyaniline)calix[4]arene of cone (cL) and partial cone (pcL) conformations were optimized by PM3 of quantum chemical method. It has been found that cL structure is more stable than pcL conformation. The stabilization energies of protonation on four aniline-nitrogen atoms of both conformations of the ligand at 6-31G energy level, were obtained. The protonations process on the cL and pcL being 7 and 24 possible pathways, respectively, were evaluated. The basicity constants of partial cone conformation of 25, 26, 27, 28-tetra(2- ethoxyaniline)calix[4]arene obtained by potentiometric titration technique, expressed in term of logalithm are log K[subscript 1] = log K[subscript 2] = 5.59, log K[subscript 3] = 4.62 and log K[subscript 4] = 4.62. For basicity constants of cone conformation was not successfully obtained.