TeTe interactions in inorganic rings with sulfur donors

Te(II) forms binuclear complexes with bridging [{SP(Ph)2}2N]− ligands and axial aryl groups with very long Te⋯Te distances, while Te(I) analogues with [S2P(R)2]− have no axial ligands and exhibit a TeTe bond. No such selenium complexes have been found, although a square-planar mononuclear derivative of [{SP(Ph)2}2N]− is available for both Te and Se. In an attempt to study the nature of the Te⋯Te interaction, a variety of theoretical approaches and basis sets was used in order to find the best way to reproduce the Te⋯Te distance in the Te(II) derivatives. DFT calculations with the ADF program provided the best answer, since MP2 calculations are more computationally demanding. While the formal oxidation state of Te is a requirement for a TeTe bond, the type of ligand strongly determines the geometry of the binuclear species. The smaller [S2P(R)2]− leads to more asymmetric species, with Te forming a normal TeS bond and a very weak one; with [{SP(Ph)2}2N]−, both TeS bonds have comparable lengths. Selenium analogues were found to behave similarly.