PUB - Publikationen an der Universität Bielefeld

Tellurium(II) dimethanethiolate, Te(SMe)(2), and tellurium(II) diethanethiolate, Te(SEt)(2), were synthesized by reaction of TeO2 and Te(OiPr)(4) with HSMe and HSEt, respectively. In the solid state, Te(SMe)(2) exhibits a cis-conformation of the methyl groups with respect to the TeS2 plane - an unprecedented situation for nonfunctionalized organotrichalcogenides - whereas Te(SEt)(2) shows a trans-conformation. Ab initio calculations performed for Te(SMe)(2) and Te(SEt)(2) show that the cis- and trans-conformers represent minima on the potential energy surface and are stabilized by intramolecular pi-type n(S)-sigma* (Te-S') orbital interactions. In the solid state, the molecules of each compound are associated through two centro-symmetric Te2S2 units with two of their neighbors, resulting in tetracoordinate Te atoms with distorted trapezoidal configurations. While the intermolecular Te...S distance increases in the sequence R = Me < Et < iPr < tBu, the length of the covalent Te-S bond decreases in the same order, a result attributed to intermolecular sigma-type n(p)(S)-sigma*(Te-S') orbital interactions. The Te-125 NMR chemical shift of Te(SR)(2) largely depends on R (R = Me, Et, iPr, tBu) and shows a nearly linear correlation with the first ionization energy of the corresponding thiol HSR. Ab initio calculations of the Te-125 NMR shifts for the model compound Te(SH)(2) (C-2 symmetry) reveal that it also depends strongly on the HSTeS torsion angle. These results can be explained by a model in which pi-type n(p)(S)- sigma*(Te-S') and n(p)(Te)-sigma*(S-H) orbital interactions determine the paramagnetic shielding of the tellurium nucleus. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 2003).