Synthesis and Characterization of Two New Asymmetrical Potentially Heptadentate (N4O3) Tripodal Schiff Base Ligands and a Theoretical Study

Abstract

Two new asymmetrical potentially heptadentate N₄O₃ Schiff-base ligands {[NCH₂CH₂CH₂N = CH(2-OH-3, 5-t-Bu₂C₆H₂)]-[ CH₂CH₂CH₂N = CH(2-OH-C₆H₄)]₂} (H₃L¹) and {N[CH₂CH₂- CH₂N = CH(2-OH-C₆H₄) [CH₂CH₂CH₂N = CH(2-OH-3, 5-t-Bu₂-C₆H₂)]₂} (H₃L²) were synthesized and characterized by microanalysis and various spectroscopic methods (IR, ¹H NMR and ¹³C NMR). The heptadentate N₄O₃ Schiff-base ligand H₃L¹ was derived from the condensation reaction of tripodal tetraamine ligand tris(3-aminopropyl)amine with 2 equiv. of salicylaldehyde and 1 equiv. of 3,5-di-t-butyl salicylaldehyde and the ligand H₃L₂ was derived from the condensation reaction of tris(3-aminopropyl)amine with 1 equiv. of salicylaldehyde and 2 equiv. of 3,5-di-t-butyl salicylaldehyde. The relative capability of these ligands to encapsulation of a lanthanide ion, herein La(III), has been theoretically studied by ab initio restricted Hartree-Fock (RHF) and DFT (B3LYP) methods. The calculation confirmed that these ligands can effectively encapsulate a lanthanide ion and enforce a sevencoordinate geometry.