The crystal structure of tetraethylammonium Tris(O-ethylxanthato)tellurate(II): An example of five-coordinate pentagonal-planar geometry

Abstract

The crystal structure of tetraethylammonium tris(O-ethylxanthato) tellurate(11), [Et₄N] [Te(S₂COEt)₃], has been determined by single-crystal three-dimensional X-ray diffraction methods. Crystals are monoclinic of space group P2₁/c with four cation-anion pairs per unit cell which has the dimensions a 8.121(1), b 18.858(2), c 19.260(2) Å and β 105.22(2)º. The structure was solved by the normal Fourier methods and was refined with anisotropic thermal parameters by a full-matrix least-squares method converging with R and R_w values of 0.061 and 0.082 for the 2404 independent statistically significant reflections collected by counter methods. The tris(ethylxanthato)tellurate(11) anion has a novel five-coordinate pentagonal-planar structure with only two of the xanthato ligands bidentate and with the Te-S bond distances having values in the range 2.503(4)-3.059(3)Å. The TeS₅ atoms are coplanar, the maximum deviation from the plane being 0.122 Å. This, together with the intra-planar S...S distances of 3.340-3.661 Å, indicates that the ligand atoms of the pentagonal plane are not over-crowded. The geometry of the anion configuration can be explained in terms of the VSEPR theory using a pentagonal-bipyramidal arrangement of the seven electron pairs in the valence shell of the tellurium.