CRYSTAL AND MOLECULAR STRUCTURE OF TRANS-TETRABROMO- AND TRANS-TETRACHLOROBIS(TETRAMETHYLTHIOUREA)TELLURIUM(4)

Both trans-tetrabromo-and trans-tetrachlorobis(tetramethylthiourea)tellurium(IV), TeX4-(C5H12N2S)2 (X = Br, Cl), are dark red substances forming orthorhombic crystals of space group symmetry Pbca and having four molecules per unit cell. Measured and calculated densities are 2.21 and 2.19 and 1.70 and 1.72 g cm-3, for the bromide and chloride, respectively. The unit cell dimensions of the bromide are a = 14.98 ± 0.03 Å b = 13.88 ± 0,03 Å and c = 10.40 ± 0.02 Å. For the chloride these are a = 14.74 ± 0.03 Å b = 13.87 ± 0.03 Å and c = 10.06 ± 0.02 Å. Diffraction data for 861 and 596 independent, observed reflections for the bromide and chloride, repesctively, were collected using Cu Kα radiation and the multiple-film Weissenberg technique. Reflection intensities were estimated visually. In determining the structure of the bromide Patterson projections on h0l and hk0 revealed the approximate positions of Te, Br, and S atoms. The positions of the C and N atoms were found by three-dimensional Fourier methods, and full-matrix, three-dimensional, least-squares refinement led to a final, conventional R value of 0.090. The refinement of the chloride proceeded, using trial atomic positions corresponding to those of the bromide structure, to an R value of 0.083. As required by tellurium's occupancy of a center of symmetry in the unit cell, the two sulfur atoms of each molecule are in trans positions. With the four halogen atoms they form a slightly distorted octahedral arrangement around the tellurium atom. The Te-S bond lengths of 2.707 ± 0.01 and 2.699 ± 0.008 Å in the bromide and chloride, respectively, are significantly longer than the sum of the covalent radii, but the Te-Br distances of 2.707 ± 0.007 and 2.686 ± 0.007 Å and the Te-Cl distances of 2.536 ± 0.008 and 2.520 ± 0.008 Å are in accord with the covalent radii sums. © 1969, American Chemical Society. All rights reserved.