Prediction of a Nine−Membered Aromatic Heterocyclic 1,4,7−triazacyclononatetraenyl anion and its Sandwich Complexes with Divalent Lanthanides

The sandwich complexes of heterocyclic ligands have attracted immense attention of scientists because of their applications in anticancer, antibacterial and antitumor activities. Moreover, lanthanide sandwich complexes possess wide range of applications as single molecule magnet, optical materials, and in spintronics and catalysis. Designing a new aromatic ring is very important for the creation of magnetically coupled one−dimensional sandwich molecular wires, which are of significant recent interests. In the present work for the first time we have theoretically proposed a nine−membered novel aromatic heterocyclic anionic ligand, 1,4,7−triazacyclononatetraenyl ion, C 6 H 6 N 3 − (tacn), associated with three hetero atoms and 10 π delocalized electrons. The aromaticity of tacn has been analyzed using NICS, HOMA and Hückel rule. Subsequently, sandwich complexes of divalent lanthanides with the tacn ligand, Ln(C 6 H 6 N 3 ) 2 (Ln=Nd(II), Pm(II), Sm(II), Eu(II), Tm(II) and Yb(II)) have been investigated. The structural properties, nature of bonding and thermodynamic stability of the predicted Ln(C 6 H 6 N 3 ) 2 complexes have been investigated using dispersion corrected density functional theory. One to one correspondence in the various properties of the predicted C 6 H 6 N 3 − ligand and Ln(C 6 H 6 N 3 ) 2 complexes with the experimentally observed corresponding C 9 H 9 − ligand and Ln(C 9 H 9 ) 2 complexes shows the feasibility of formation of the predicted Ln(C 6 H 6 N 3 ) 2 complexes.