Distinguishing between Coordination and Spodium Bonds in the Dinuclear Cadmium(II) Complex of Lawesson’s-Derived Phosphonodithioates

Abstract

In this study, Lawesson’s-derived phosphonodithioates and associated cadmium(II) complex, with the molecular formula of (4-C₆H₄OMe){4-C(CH₃)₃C₆H₄O}PS₂NHEt₃ (1), (4-C₆H₄OMe){4-C(CH₃)₃C₆H₄O}PS₂Na (2), and [Cd{S₂P(OC₆H₄(4-C(CH₃)₃))(4-C₆H₄OMe)}₂] (3), were assembled and characterized structurally. Crystallographic studies indicate that 1 and 3 crystallize in the triclinic P̅1 space group. The solid-state structure analysis revealed that complex 3 is a centrosymmetric dinuclear species. The two symmetry-related Cd atoms are simultaneously bridged and chelated by sulfur atoms of four S₂P(OC₆H₄(4-C(CH₃)₃))(4-C₆H₄OMe) anions, thus bonding with four S atoms in a distorted tetrahedral environment. As a result, an eight-membered core with a “twisted chair” conformation is joined to two four-membered chelate rings. Intramolecular spodium bonds (SpBs) are established between the S atom of the bridging ligands and the Cd(II) center. The theoretical studies (viz., density functional theory (DFT), quantum theory of atoms in molecules (QTAIM), and noncovalent interaction plot (NCIplot)) have been performed to investigate the existence of SpBs in the synthesized complex. Moreover, Hirshfeld surface analysis has been directed to perceive the intermolecular noncovalent contacts within the crystal lattice.