Some molecular structures by electron and x-ray diffraction

Abstract

Two polycyclohydrocarbons, norbornane and the compound C12H14 of De Vries and Winstein, were investigated by electron diffraction. For both molecules the C-C bond was found to be lengthened from the normal value of 1.54 A. Bond strain calculations were made for both molecules. An electron diffraction investigation of ferrocene confirmed the proposed sandwich structure. The following distances for a model with D5d symmetry were derived by the correlation method: Fe-C, 2.064 A; C-C, 1.440 A. Both models in which the rings were allowed to rotate with a small potential barrier and models in which the inter-ring C...C distances were assigned a moderately large vibrational temperature factor constant, with no rotation, were found to be consistent with the visual data. The crystal structure of cyclopentadienyl manganese tricarbonyl was studied by X-ray diffraction. The crystal was treated as a heavy atom problem and three-dimensional methods were used. Anisotropic temperature factors were calculated from a difference Fourier synthesis. The positional parameters were refined by least squares. The Mn(CO)3 part of the molecule has nearly trigonal symmetry and the ring was found to be nearly planar. The packing of the molecules approximates a cubic closest packed array of spheres. Cyclopentadienyl nickel nitrosyl was investigated by electron diffraction. The method of least squares was used in order to refine the parameters and to estimate the limits of error. Both models with a linear Ni-N-0 bond and models with a bent Ni-N-0 bond were found to be acceptable. Bond distances in metal carbonyls and related compounds are discussed.