Quantum chemical calculations on structure and bonding of macrocyclic complexes of Li(I) and Na(I)

Abstract

Abstract Quantum chemical calculations within the ab initio Hartree-Fock framework have been carried out for the complexes of Li(I) and Na(I) ions with both 1,4,7,10-tetraaza- and 1,4,7,10-tetraoxa-cyclododecane, optimizing the conformation of ligands and complexes. In agreement with experimental findings, ab initio calculations predict the alternate and maxidentate as being the most stable structures of the poly-N and poly-O ligands respectively. These conformations are also maintained in both complexes. The conformational changes to suit the metal being complexed consume only minor energies. When compared to the open chain analogues, the results show that much more energy input is necessary to change the structure of the open chain ligands to the optimal form for metal binding, especially in the case of polyethers. It is understood, therefore, that the peculiar stability of the complexes with macrocyclic ligands is mainly due to the rigid pre-trained conformation of theses specific ligands types, «containing» already the amount of strain energy which otherwise reduces the gain of energy by metal bonding considerably.