STRUCTURAL STUDIES OF (PI-C5H5)2MX2 COMPLEXES AND THEIR DERIVATIVES - STRUCTURE OF (1,1'-TRIMETHYLENE-PI-DICYCLOPENTADIENYL)HAFNIUM DICHLORIDE
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(1,1-Trimethylene--dicyclopentadiene)hafnium dichloride, (CH2)3(C5H4)2HfCl2, is orthorhombic, space group Pbca, and isomorphous with the corresponding zirconium compound. The unit cell dimensions are a = 8.177 (3) , b = 13.916 (4) , and c = 22.425 (9) , with Z = 8. The structure was determined from three-dimensional X-ray data (1797 independent reflections), obtained by means of an automated four-circle diffractometer, and refined anisotropically to an R of 0.029. The coordination about the hafnium atom is that of a distorted tetrahedron comprised of the chlorine atoms and the centroids of the -cyclopentadienyl rings. The Cl-Hf-Cl bond angle is 95.87 (8) and the centroid-Hf-centroid angle 129.5. The Hf-Cl bond distances are 2.417 (3) and 2.429 (2) . These are slightly smaller than the corresponding bond distances in the zirconium complex and are in agreement with the sum of the Pauling radii. Distances from the hafnium atom to the ring centroids are 2.170 and 2.181 and the range of Hf-C distances is 2.459-2.501 . The carbon-carbon bond distances within the cyclopentadiene rings average 1.404 A and range from 1.368 (17) to 1.438 (12) . These parameters not only establish the pentahapto nature of the metal-ring bonding but indicate that when the thermal motion of the rings is reduced by the constraints of the exocyclic bridge, the C-C bond lengths have a narrower range and calculate closer to the expected value of 1.41 . 1974, American Chemical Society. All rights reserved.
