Crystal and molecular structure of niobocene carbonyl chloride. pi. -(C/sub 5/H/sub 5/)/sub 2/Nb(CO)Cl and refinement of the structure of niobocene carbonyl hydride. pi. -(C/sub 5/H/sub 5/)/sub 2/Nb(CO)H

The crystal structure of Cp/sub 2/Nb(CO)H (I), which was previously interpreted on the basis of photographic experimental data (1), has been refined, and the structure of Cp/sub 2/Nb(CO)Cl (II) has been determined (Synthex P2/sub 1/ autodiffractometer, lambda Mo K..cap alpha.., graphite monochromator, refinement by the anisotropic least-squares method on the basis of 2175 reflections to R = 0.052 for I on the basis of 2230 reflections to R = 0.053 for II). The hydride hydrogen atom in compound I was located on a difference Fourier synthesis, and the hydrogen atoms of the pentadienyl groups were assigned according to the HPOSN program on the basis of a planar ring model and a C-H distance equal to 1.03 A and were not refined. Both complexes have a wedged sandwich geometry with an eclipsed conformation of the Cp rings. In compound I Nb-C(C/sub 5/H/sub 5/)av = 2.37, C-C(C/sub 5/H/sub 5/)/sub av/ = 1.39, Nb-H = 1.69(10), Nb-C(CO) = 2.039(7), C-O = 1.15(1) A, and < NbCO = 177.8(6)/sup 0/. The angle between the C/sub 5/H/sub 5/ planes is 38/sup 0/, and the minimal nonbonded C...C distance is 3.19 A. In compound II Nb-C(C/sub 5/H/sub 5//sub av/ = 2.37, C-C(C/sub 5/H/sub 5/)/sub av/ =more » 1.41, Nb-Cl = 2.557(3), Nb-C(CO) = 2.03(1), C-C = 1.15(1) A, < NbCO = 175.2(9), and < C(O)NbCl = 94.0(3)/sup 0/. In the structure there are short H...Cl intermolecular contacts measuring 2.6 A. The angle between the C/sub 5/H/sub 5/ rings is 44.4/sup 0/. The minimal C...C distance is 2.92 A. The crystals of compound I are triclinic: a = 5.972(2), b = 7.965(2), c = 11.569(4) A, ..cap alpha.. = 79.48(3), ..beta.. = 76.73(2), ..gamma.. = 68.01(2)/sup 0/, space group P anti 1, Z = 2. The symmetry of compound II is monoclinic: a = 9.123(1), b = 10.288(1), c = 11.679(1) A, ..beta.. = 99.71(1)/sup 0/, space group P2/sub 1//n, Z = 4.« less