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Determination of the crystal structures of some inogranic compounds by X-ray diffraction Williston, Carolyn Susan

Abstract

Dimethyltellurium diiodide is known in two forms; the crystal structure of the β-form has been determined by X-ray diffraction; Mo-Kα scintillation counter data were used for this analysis in which the heavy atoms were located from the Patterson function, the carbon atoms by a difference synthesis and refinement was by least-squaresmethods. β-dimethyltellurium diiodide is ionic, [Me₃Te]⁺ [MeTeI₄]⁻, and is built up from trigonal pyramidal Me₃Te⁺ cations with Te - C = 2.07 Å, C - Te - C = 95°, and square pyramidal MeTeI₄⁻ anions with Te - C = 2.15 Å, Te - I = 2.84 - 2.98 Å. The ions are bridged by four weak Te... I interactions (distances 3.84, 3.88, 3.97, 4.00 Å), which complete a distorted octahedral environment around each tellurium atom. The crystal and molecular structures of 2-biphenylylferrocene and 4-biphenylylferrocene have been investigated in order to compare the configuration of the rings of the biphenyl and ferrocene groups in these two molecules. The structure of 2-biphenylylferrocenje, has been determined with visual Gu-Kα data. The iron atom position was found by Patterson methods, the carbon positions from successive Fourier summations. The positional and thermal parameters were refined by least-squares. The cyclopentadienyl rings are eclipsed, the first six-membered ring of the biphenyl group is rotated 43° out of the cyclopentadienyl plane and the outer six-membered ring is rotated 58° out of the plane of the first six-membered ring. These rotations relieve the strain which would exist in a planar model for the C₅H₄ . C₆H₄ . C₆H₅ group. The mean bond distances are Fe - G = 2.05 Å, C - C (cyclopentadienyl) = 1.44 Å. Using Fe-Kα scintillation counter data, the structure of 4-biphenylylferrocene has been determined by Patterson and Fourier methods and refined.by least-squares. The two crystallographically independent molecules in the unit cell have slightly different conformations. In one the cyclopentadienyl rings are oriented about midway between the eclipsed and staggered conformations and the first six-membered ring is rotated 6° out of the plane of the cyclopentadienyl ring to which it is bonded, with the second six-membered ring rotated a further 9°. In the second molecule the cyclopentadienyl rings are only about 5° form the fully eclipsed position and the six-membered ring rotations are 0° and 10°. The mean bond distances are Fe-C = 2.07 Å, C-C (cyclopentadienyl) = 1.48 Å, C-C (biphenylyl) = 1.43 Å, C-C (between rings) = 1.48 Å. The intermolecular separations correspond to, van der Waals' interactions.

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