A neutron diffraction study of bis(cyclopentadienyl)(methyl)(methylene)tantalum(V) at 15 K

Abstract

[Ta(C5H5)2(CH2)(CH3)], Mr = 340-206, monoclinic, Pljc, a = 6-492 (1), 6 = 11-539 (2), c= 15-174(2) A, P = 117-33 (2)°, V= 1009-8 (3) A3, Z = 4, Dx = 2-238 Mg m-3, neutrons, X = 1-1617(2) A, // = 0-2473 mm"1, F(000) = 122-68 fm. T= 15(0-5) K. The structure has been refined based on 2446 reflections to yield an unweighted R value based on F2 of 0-043. The molecule has approximate Cs point symmetry. All C—H bond distances have been determined with e.s.d.'s < 0-003 A. The mean C - H distance [ 1 - 091 (4) A] in the methyl group is slightly longer than that in the methylene group [1-081 (5) A], while therespective H-C-H angles are 107-8(3)° (methyl, mean value) and 112-3(2)° (methylene). The Ta-C methylene distance is 2-039 (1) A, corresponding to a full double bond, 0-229 (1) A shorter than the Ta-C methyl distance of 2-268 (1) A. The cyclopentadienyl rings have an envelope geometry and exhibit small systematic deviations of the C - C bond distances from the mean value of 1-419 A; by contrast, the ring C—H distances are equivalent, with a mean value of 1-084(1) A.