The crystal and molecular structure of Rh(ƞ5-C5(CH3)5)(CO)2 has been determined from a single-crystal X-ray diffraction study. The entire molecule approximates bilateral symmetry with the molecular mirror plane normal to the cyclopentadienyl ring and bisecting the Rh(CO)2 fragment. The cyclopentadienyl C(ring)-C(ring) bond lengths consist of one short bond of 1.384 (8) Å adjacent to two long bonds of 1.445 (8) and 1.447 (7) Å, with the remaining two bonds having intermediate lengths of 1.412 (8) and 1.410 (7) A. These bond distances are within one standard deviation of the distances found in the analogous cobalt complex. In addition, the cyclopentadienyl ring exhibits a slight symmetric distortion from planarity that significantly reflects the bonding between the ring and the metal. Molecular orbital calculations on an idealized geometry of Rh(ƞ5-C5H5)(CO)2, in which the cyclopentadienyl ring is given symmetry, illustrate the electronic origin of the ring distortion. Calculated three-dimensional electron density maps show that the bonding of the ring to the metal is slightly dominated by a “dialkene” type interaction in which a single e1- orbital of the ring donates into an empty inplane metal d orbital of the d8 Rh(CO)2+ portion of the molecule. The distortions of the ring are consistent with the character of this orbital. The title compound crystallizes in the monoclinic space group P21/n with a = 7.765 (3) Å, b = 10.741 (3) Å, c = 15.267 (7) Å, β = 98.75 (3)°, and a calculated density of 1.551 g cm-3 for Z = 4. Full-matrix least-squares refinement with varying positional and anisotropic thermal parameters for the non-hydrogen atoms and idealized positional and isotropic thermal parameters for the hydrogen atoms converged at R1 = 0.0339, R2 = 0.0418, and GOF = 1.6818 (n = 136) for the 1610 independent reflections (I ≥ 3σ(I)) collected with Mo Kα radiation over the 2Θ range of 4° ≤ 2Θ ≤ 50°.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry