3-(2-pyridyl)-5-(4-chlorophenyl)-1,2,4-triazine as a ligand: Synthesis of three lead(II) complexes, a spectroscopic and structural study using experimental and theoretical methods

Abstract

Three new Pb(II) complexes of the ligand 3-(2-pyridyl)-5-(4-chlorophenyl)-1,2,4-triazine (pcpt) and different anionic co-ligands (1: bromide, 2: iodide and 3: isothiocyanate) were synthesized and characterized by elemental (CHN) analysis, FT-IR and 1H NMR spectroscopy and single crystal X-ray diffraction (SC-XRD). Considering only strong primary coordination bonds, the Pb(II) centres in complexes 1 and 2 are holodirectionally and in 3 hemidirectionally coordinated by the organic pcpt ligands due to stereochemical inactivity (1, 2) and activity (3) of the lone electron pair. The primary coordination sphere in 3 is sterically suitable for establishing interactions at longer distances, where the Pb centre acts as Lewis acid. Thus, all the Pb centers participate in Pb⋅⋅⋅Cl tetrel interactions, which together with secondary interactions of the ligands extend the structures into 1D supramolecular assemblies. A Hirshfeld surface inspection, along with the natural bond analysis (NBO), quantum theory of atoms in molecules (ATAIM), molecular electrostatistic potential (MEP) surface, and theoretical vibrational analysis at B3LYP/Def2-TZVP level of theory were conducted for the sake of further investigation of the non-covalent interactions in complexes 1–3. An enrichment ratio is also calculated for the chemical species to determine the tendency of their interactions in the crystal packing. The theoretical values obtained from the DFT at B3LYP/Def2-TZVP level of theory ensure that the expected consequences match the experimental findings. The QTAIM calculations allow the estimation of the strength of the primary and secondary/tetrel interactions and to propose the theoretical criteria based on the |VBCP|/GBCP, HBCP/ρBCP, and DI parameters for distinguishing the interactions. The MEP calculations confirmed the presence of a σ-hole in the proximity of the PbII centers.