Establishing σ-hole tetrel bonds by hemidirected lead(II) phosphonodithioates

This study explores the ability of hemidirected lead(II) centres to form σ-hole tetrel bonds (TtBs) with electron-rich atoms. Lawesson's reagent was used to produce arylphosphonodithioates and their corresponding lead(II) complexes with the formulas (4-C₆H₄OMe){4-CH₃C₆H₄O}PS₂NHEt₃ (1), (4-C₆H₄OMe){4-CH₃C₆H₄O}PS₂Na (2), and Pb[S₂P{OC₆H₄(4-CH₃)}{C₆H₄(4-OCH₃)}]₂ (3). The molecular structures were studied by X-ray crystallography, revealing that 1 crystallizes in the orthorhombic crystal system with the P2₁2₁2₁ space group and 3 in the monoclinic crystal system with the P2₁/c space group. In complex 3, the Pb(II) center exhibits a hemidirected coordination sphere, bonded to three sulfur atoms and possesses a stereochemically active lone pair, resulting in a distorted trigonal pyramidal geometry. The presence of bulky ligands in complex 3 limits its coordination, generating an open region around Pb that facilitates the formation of directional σ-hole TtBs, specifically Pb⋯S and Pb⋯π interactions. Molecular electrostatic potential (MEP) analysis reveals a pronounced σ-hole at the Pb center, which facilitates directional TtBs. These interactions were further characterized and energetically evaluated using quantum theory of atoms in molecules (QTAIM) and non-covalent interaction (NCI) plot analyses. The supramolecular architecture of complex 3 features a self-assembled dimer stabilized by Pb⋯S TtBs, forming an eight-membered quasi-cyclic motif. Additionally, Hirshfeld surface analysis (HSA) highlights the role of TtBs and other non-covalent contacts in the crystal packing of complex 3. Overall, this work underscores the importance of σ-hole interactions in the design and assembly of Pb(II)-based coordination complexes and provides valuable insights for advancing supramolecular and crystal engineering strategies in modern coordination chemistry.