Experimental and Theoretical Study of Tetrel Bonding and Noncovalent Interactions in Hemidirected Lead(II) Phosphorodithioates: An Implication on Crystal Engineering

The importance of tetrel bonds (TtBs) in spontaneous selfassembly has been highlighted in two new lead(II) complexes: i.e. Pb[S2P{OC6H4(4-C(CH3)3)}2] 2 (1) and Pb[S2P{OC6H4(4-C2H5)}2] 2 (2), which were successfully isolated and characterized by FT-IR, UV-vis and multinuclear NMR (31P, 1H and 13C) spectroscopy. The structures of both complexes have been confirmed by single-crystal X-ray diffraction analyses. Interestingly, lead is coordinated by three sulfur atoms in 1 but by four sulfur atoms in 2, due to stereochemically active lone pair electrons, thus leading to trigonal-pyramidal and tetragonal-pyramidal geometries, respectively. Complex 1 is the first example of a lead(II) dithiophosphate wherein the lead(II) center is coordinated to three S atoms. These complexes are stabilized at a lower coordination number and display hemidirected structures that allow forming s-hole bonds. The lead(II) center establishes short contacts with sulfur atoms to form Pb center dot center dot center dot S TtBs that contribute to the construction of a self-assembled dimer in 1 but to a supramolecular polymer in 2. The supramolecular assemblies are further stabilized by Pb center dot center dot center dot p TtB interactions. The attractive nature of TtBs has been studied by DFT calculations and characterized using a combination of Bader's quantum theory of atoms-in-molecules (QTAIM) and noncovalent interaction plot (NCI plot) index based on a reduced density gradient (NCI-RDG) analysis. A systematic Hirshfeld surface analysis facilitates a comparison of intermolecular interactions such as C-H center dot center dot center dot p, p center dot center dot center dot p, Pb center dot center dot center dot S, and Pb center dot center dot center dot p in both complexes, which play a crucial role in the crystal engineering.