The nature of the chemical bonding and crystallography of π-cyclopentadienyl-hexakis(trifluoromethyl)benzene rhodium

A three-dimensional X-ray analysis of the crystal structure of $\pi$-cyclopentadienyl-hexakis-(trifluoromethyl) benzene rhodium, based on 2119 independent reflexions, is described. The crystals are monoclinic, a = 9.48 $\overset{\circ}{\mathrm A}$, b = 12.59 $\overset{\circ}{\mathrm{ A}$, c = 17.79 $\overset{\circ}{\mathrm A}$, $\beta$ = 114.75$^\circ$, Z = 4, space group P2$_{1/C}$. The final residual factor is 0.096, the Rh-C bond distances having standard deviations which range from 0.014 to 0.027 $\overset{\circ}{\mathrm A}; bond lengths in the benzene ligand (\overline{$\sigma$} = 0.020 $\overset{\circ}{\mathrm A}$), together with the ring conformation, illustrate a novel form of bonding for arene complexes of transition metal ions. The bonding of the $\pi$-cyclopentadienyl anion to the rhodium appears to be asymmetric and is related to that in similar molecules. Valence bond and molecular orbital descriptions of the electronic structure of the molecule are summarized together with those intra- and inter-molecular non-bonded interactions which stabilize the conformation of the -CF$_3$ groups.