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RESEARCH PRODUCT

Tellurium( II ) Dialkanethiolates: n p (S)‐σ*(Te−S′) Orbital Interactions Determine the 125 Te NMR Chemical Shift, and the Molecular and Crystal Structure

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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).