Electron density distribution in vanadocene (η5-C5H5)2V and mixed metallocenes (η5-C5H5)M(η5-C7H7) (M = Ti, V, or Cr) and (η5-C5H5)Ti(η8-C8H8). Effect of the nature of the cyclic ligand on the character of the M-(π-ligand) bond

The electron density distribution and atomic displacements were analyzed based on the results of precision low-temperature X-ray diffraction studies of a series of isostructural (Pnma, Z = 4) mixed metallocenes (eta (5)-C5H5) M(eta (5)-C7H7) (M = Ti, V, or Cr) and (eta5-C5H5)Ti(eta (8)-C8H8). The barriers to rotation of the cyclic ligands were evaluated based on rms libration amplitudes. Analysis of the deformation electron density demonstrated that the character of the M-(pi -ligand) chemical bond depends substantially both on the nature of the metal atom and the size of the ligand. Lowering of the local symmetry of the (eta (5)-C5H5)M(eta (5)-C7H7) complexes to Cs leads to distortion of the cylindrical symmetry of the electron density distribution observed in vanadocene (eta (5)-C5H5)(2)V and titanocene (eta (5)-C5H5)Ti(eta (8)-C8H8).