A self-consistent molecular mechanics force field for complexes of the type [M(Cp’)(2)Cl-2] (M = Ti, Zr, Hf; Cp’ = a substituted cyclopentadienyl ligand) has been developed. Force constants were derived from vibrational data of the [M(Cp)(2)Cl-2] complexes. The force field reproduces known structures with high precision, and it was demonstrated that crystal packing forces can affect the orientations of the Cp’ rings and the conformations of substituents. Crystal packing calculations reproduce structures in the crystal well. Systems where the Cp’ rings are joined by aliphatic carbon straps and where the Cp’ rings are fused to six-membered rings containing aliphatic carbon atoms generate diastereomers due to the chiral puckering of the strap, the six-membered rings, and the chiral binding of the Cp’ rings. It is calculated that these various conformations are close in energy and are likely to interchange rapidly in solution. When the strap is chiral the energetic interplay between these conformations can lead to preferred binding of prochiral Cp’ ligands. Interplay of these energetically closely spaced conformations is likely to guide consideration of the steric origins of stereoselective reactions promoted by derivatives of these complexes. It is shown that the conformation observed in the crystal is generally not the most stable.