An insight into triel bonds in O,O'-diarylphosphorodithioates of thallium(I): Experimental and theoretical investigations

The vital role of triel bonding (TrB) has been highlighted in two new thallium compounds i.e. Tl+[{(4-C2H5)C6H4O}2PS2]2- (1) and Tl[{(4-(CH)CH3)2C6H4O}2PS2]2 (2). These new compounds have been characterized by elemental and spectral analyses. The crystal structure of 1 and 2 belongs to monoclinic and triclinic system with space group P21/c and Pī, respectively. Interestingly, compound 1 exists in ionic form and stabilized through intramolecular Tl⋯S (TrBs) interactions wherein thallium atom is symmetrically positioned in the cleft of ligand with longer Tl–S distances. In compound 2, the thallium atom is coordinated to one sulfur atom and other sulfur atom participates in TrB interactions. Both the compounds also exhibit intermolecular Tl⋯S, Tl⋯π (TrBs) and C-H⋯Tl (anagostic) interactions which assist to form unique supramolecular architectures owing to large size as well as coordinative unsaturation on the thallium. These non-covalent TrB interactions were authenticated by Hirshfeld surface analysis (HSA) and Density functional theory (DFT) calculations using the quantum theory of atoms-in-molecules (QTAIM) and non-covalent interaction plot (NCI Plot) index methods. TrBs involving Tl have been scarcely described in the literature; therefore this manuscript provides valuable insight into the importance of these unprecedented TrBs in the solid state.