Terpyridine Zn(II) azide compounds: Spectroscopic and DFT calculations

Square-pyramidal Zn(II) azide complexes with the formula of [Zn_n(N₃)_2nL] (n = 1; L = 4′-(2-pyridyl)-2,2′:6′,2′'-terpyridine (L^Py), 4′-(4-phenylmorpholine)-2,2′:6′,2′'-terpyridine (L^Morph), and n = 2; L = 1,4-bis(2,2′:6′,2′'-terpyridin-4′-yl)benzene (L^BPY)) were synthesized, and structurally characterized using different spectroscopic and analytical tools. Ground-state geometry optimization and harmonic vibrational analysis were carried out at two different levels of theory (B3LYP/LANL2DZ and CAM-B3LYP/def2-SVP) to gather insights into the local minimum structures. Natural bond orbital (NBO) analyses revealed that the electronic population of the 3d orbitals of Zn(II) ion is corresponding to the oxidation state of Zn(I), not Zn(II), in agreement with the ligand to metal charge transfer. Molecular electrostatic potential energy maps showed that the azido ligand may act as a nucleophile in the cycloaddition coupling with electron poor dipolar molecules. The electronic structure and transitions were investigated by executing time dependent density functional theory (TDDFT) calculations.