Systematic Investigation of Electronic and Molecular Structures for the First Transition Metal Series Metallocenes M(C5H5)2 (M = V, Cr, Mn, Fe, Co, and Ni)

The electronic structures of the first-row transition-metal metallocenes, MCp2 (M = V, Cr, Mn, Fe, Co, and Ni), have been studied using a broad range of density functional methods with flexible double-ζ plus polarization (DZP) basis sets. Geometrical parameters of the D5h and D5d conformations (and structures of lower symmetry for CrCp2 and CoCp2) were fully optimized. For the ferrocene system, best characterized experimentally, the B3LYP, BLYP, and BP86 methods give structures in good agreement with experiment. For the D5h−D5d energy difference, the same three methods predict 0.75 kcal/mol (B3LYP), 0.99 kcal/mol (BLYP), and 1.13 kcal/mol (BP86). The cyclopentadienyl rings are very nearly planar; the angles of the C−H bond out of the Cp ring are less than 1° for all metallocenes except ferrocene. The C−H bonds are bent slightly away from the metal for V and Mn, slightly toward the metal for Fe and Ni, and virtually not at all from chromocene. According to the energetic and vibrational analyses, the D5h co...