A Theoretical Study on the Structural, Electronic and Optical Characteristics of Tetraaza Macrocyclic

Pd (II) complex containing tetraaza macrocyclic ligand has already been an important
topic of current research studies, especially in catalysis, waste treatment application,
and biomedical. The most unique properties of macrocycles containing nitrogen atoms
are high selectivity towards transition metal ions and a high tendency to form
macrocyclic compounds. The established method of synthesising tetraaza macrocyclic
ligand by introducing a transition metal ion as a templating agent has demonstrated
difficulties in the decomplexation process because template ions are too stable. Later,
one pot synthesis of the non-template has been introduced resulting in protonated
tetraaza macrocyclic ligand and metal complex. However, until today, there are limited
theoretical studies that specifically reported on metal-ligand interaction in
complexation. Therefore, this study examined the structure of the Pd(II) tetraaza
macrocyclic ligand and further explored its electronic properties through density
functional theory (DFT) calculation. The molecular geometry shows that the Pd(II)
atom successfully fits in the macrocyclic ligand and metal-ligand interaction contributes
to the stability of the Pd (II) tetraaza macrocyclic ligand. Then, the optical properties of
Pd(II) tetraaza macrocyclic ligand were investigated at excited state using timedependent
density functional theory (TD-DFT) in gas medium observed frontier
molecular orbitals indicate high electron mobility since only little energy is required for
the electron transfer process. The optical responses on Pd (II) tetraaza macrocyclic
ligand in hexane, toluene, chloroform, methanol, acetonitrile, and water environment
using integral equation formalism of polarizable continuum model (IEF-PCM) show
significant changes of the energy gap, absorption peaks, and hyperpolarizability values
compared in gas medium.