Te-Te interactions in inorganic rings with sulfur donors

Te(II) forms binuclear complexes with bridging [{S=P(Ph)(2)}(2)N](-) ligands and axial aryl groups with very long (TeTe)-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)}(2)N](-) is available for both Te and Se. In an attempt to study the nature of the (TeTe)-Te-... interaction, a variety of theoretical approaches and basis sets was used in order to find the best way to reproduce the (TeTe)-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)}(2)N](-), both Te-S bonds have comparable lengths. Selenium analogues were found to behave similarly. (C) 2003 Elsevier B.V. All rights reserved.