Synthesis, spectral and luminescence study, crystal structure determination and DFT calculation of binuclear...

Binuclear palladium(II) complexes with metal-metal (d⁸-d⁸) bonding interaction were synthesized by reactions of the 1-methyl-1H-1,2,3,4-tetrazole-5-thiol (Hmtzt) or a mixture of Hmtzt and 1,3-propanediamine (1,3-pda) ligands. Complex [Pd₂(μ-mtzt)₄]·2CH₃CN (1) was synthesized by the reaction of Pd(OAc)₂ with Hmtzt dissolved in acetonitrile and complex [Pd₂(μ-mtzt)₂(mtzt)₂(1,3-pda)] (2) was synthesized by reaction of a mixture of Hmtzt and 1,3-propanediamine (dissolved in methanol) with PdCl₂ (dissolved in acetonitrile) and were identified through elemental analysis, IR, UV-Vis, ¹H NMR, luminescence spectroscopy as well as single-crystal X-ray diffraction method. A single-crystal of complex 1 shows that two Pd(II) centers are linked together by four bridging tetrazole ligands providing a paddle wheel-like arrangement. Also a crystal structure of complex 2 shows that this complex possesses a symmetric structure in which one Pd atom is tetra-coordinated by four sulfur atoms to forms PdS₄ and other Pd atom is tetra-coordinated by four nitrogen to forms PdN₄ coordination sphere. Density functional theory (DFT) was performed in this study for the Hmtzt ligand and binuclear palladium(II) complexes (1) and (2). The DFT calculation shows Pd^II-Pd^II bond lengths of 2.831 and 3.086Å in complex 1 and 2, respectively which are close to the observed bond lengths of 2.802(11) and 3.0911(17)Å from single-crystal X-ray structure. The optimized geometry of the complexes is shown good agreement by X-ray data. Structural properties and molecular descriptors including bond lengths, bond angles, chemical hardness, dipole moment, HOMO-LUMO energy levels, electron transfer were analyzed. The IR spectroscopy was performed using VEDA4 software and UV-Vis spectra were analyzed using time-dependent density functional theory (TD-DFT) method. The theoretical and experimental data were also compared with each other.