Effect of a lone electron pair and tetrel interactions on the structure of Pb(II) CPs constructed from pyrimidine carboxylates and auxiliary inorganic ions

Abstract

Three new Pb(II) coordination polymers (CPs) of pyrimidine-2-carboxylate ligand and different anionic co-ligands (perchlorate, chloride and nitrate) were synthesized and characterized by physicochemical (CHN, FT-IR, TG) and structural (SC-XRD) methods. Considering only strong primary coordination bonds the Pb(II) centres in all three complexes are hemidirectionally coordinated by organic ligands due to stereochemical activity of a lone electron pair. The Pb nodes and ligand linkers formed single- or double-layered 2D networks with honeycomb-like topology. The primary coordination sphere is sterically suitable for establishing the interactions at longer distances, where Pb centre act as Lewis acid. The MEP calculations confirmed the presence of a σ-hole in the proximity of Pb centres. Thus, all the Pb centres participate in Pb···O or Pb···Cl tetrel interactions with auxiliary inorganic ions, which together with secondary interactions of ligands and water molecules extended the structures into 3D supramolecular assemblies. The QTAIM calculations allowed for estimation of the energy of primary and secondary/tetrel interactions and to propose the theoretical criteria based on the |VBCP|/GBCP, HBCP/ρBCP, and DI parameters for distinguishing among interactions.