| Popis: |
Calculations using ab initio restricted Hartree–Fock molecular orbital (RHF MO) theory and the density functional theory (DFT) are reported for several structural isomers of hexa-aza macrocycles 1 – 3 containing 2,2′-bipyridine and 1,10-phenanthroline, as well as their lithium complexes. Based on the computational results, we describe the geometries, imine/amine tautomerism, and lithium complexation of these hexa-aza macrocycles. Metal-free macrocycles have the most stable imine form with planar structures, whereas their lithium complexes tend to be in the amine form. We discuss protonation/deprotonation processes with proton transfer in a cavity of macrocycles as a means of interpreting imine/amine tautomerism. Deprotonation and the subsequent geometric changes in tautomeric isomers lead to structural changes, i.e. macrocycles 2 and 3 having 2,2′-bipyridines become non-planar; this theoretical result is consistent with observed experimental behaviors. The present results indicate that unlike macrocycle 1 , macrocycles 2 and 3 with 2,2′-bipyridine have the capacity for amine/imine tautomerism, as well as the ability to form complexes with lithium. |
Full Text from ScienceDirect