Structure of vanadocene in the temperature interval 108-357 K and the nature of the ring disorder.
The crystal structure of vanadocene, bis(h5-2,4-cyclopentadien-1-yl)vanadium, Cp2V, was studied at four temps. 108, 170, 297 and 357 K by x-ray diffraction to elucidate the nature of the Cp-ring disorder and compare the results obtained with similar data for formally isostructural ferrocene, cobaltocene and nickelocene. A careful anal. of the anisotropic displacement parameters (ADP's) for Cp2V showed that at 108 K the crystal structure is ordered (staggered Cp2V mols. occupy centers of symmetry in the space group P21/n, Z = 2), which distinguishes vanadocene from its formal analogs and some Cp-ring disorder starts at .apprx.170 K. A model of this disorder is proposed with two distinct orientations of the ring, differing in temp.-dependent occupancy factors and by a rotation in the ring plane of almost 36 Deg. The fractional contributions of the 2nd (minor) ring orientation are 0.05, 0.17 and 0.35, resp., at 170, 297 and 357 K. The energetic characteristics of the ring rotation motion in the Cp2V crystal were estd. from ADP anal. and compared with similar data for other 3d-metallocenes.
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