An analysis of crystal structures of the type (eta5-C5H4R)MLx (x = 1-5
) has been undertaken. A measure of the steric and electronic effects
associated with L and R has been assessed from the arrangement of the
L ligands relative to R and from the bending of R out of the cyclopent
adienyl plane. The analysis revealed that when L and R were large, ste
ric effects were dominant and the preferred conformer was such that L
and R avoided each other as far as possible. Steric effects for small
L and R were significant when x was large. For instance L groups were
always staggered with respect to R for x = 4 but for x = 2 both stagge
red and eclipsed conformers were observed. Thus electronic factors wer
e only dominant for a limited number of structures in which L, R and x
were small. The results thus confirm an earlier proposal (N. J. Covil
le, K. E. du Plooy and W. Pickl, Coord. Chem. Rev., 116 (1991) 1) that
significant steric interactions are anticipated between the ring and
the ligand set in (eta5-C5H4R)MLx complexes.