Polymorphism of Palladium(II) Complexes : Crystal Structure Determination, Luminescence Properties, Hirshfeld Surface Analyses and DFT/TD-DFT Studies

Two luminescent polymorphs based on a new Pd(II) complex [Pd(mtzt)(2)(en)] (mtzt=1-methyl-1H-1,2,3,4-tetrazole-5-thiol and en=ethylenediamine) have been synthesized and characterized by FTIR, UV/Vis, elemental analysis,(HNMR)-H-1 and single-crystal X-ray diffraction analysis. The X-ray structural analysis indicated that in the structures of these polymorphs Pd(II) cation is four-coordinated in a distorted square planer configuration by two tetrazole rings in the cis-positions, two nitrogen atoms of chelated ethylenediamine ligand. The dihedral angles between the planes of the tetrazole rings of polymorphs (1) and (2) are 72.01 and 77.70 degrees, respectively. Moreover, in these polymorphs, intermolecular interactions C-H horizontal ellipsis N, C-H horizontal ellipsis S, and N-H horizontal ellipsis N hydrogen bonds, are effective in the stabilization of the crystal structures. The present study reports a detailed analysis of Hirshfeld surfaces, facilitating a comparison of intermolecular interactions in the supramolecular structure. The geometries of polymorphs (1) and (2) are optimized with B3LYP-D3/TZVP method, and analyzed with natural bond orbital (NBO), then their UV/Vis spectra are calculated with time-dependent density functional theory (TD-DFT) method. The IR spectroscopy was performed using VEDA4 software and compared with the experimental values. Quantum chemical parameters are: such as E-HOMO, E-LUMO, energy gap, chemical hardness (eta), and dipole moment (mu), and the frontier molecular orbital properties.