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By using broken-symmetry hybrid-DFT (UB3LYP and UB2LYP) calculation, the effective exchange integrals (J values) of [Cr(C5(CH3)5)2]+[TCNE]−[Cr(C5(CH3)5)2]+ and [Mn(C5(CH3)5)2]+[TCNQ]−[Mn(C5(CH3)5)2]+ were determined theoretically. Those calculated models were reduced to 3-spin-sites models from X-ray crystallographic data of charge transfer 3D crystal. The calculated results showed that effective exchange integrals were positive and the signs of spin densities on the cyclopentadienyl rings were negative. These results supported the so-called McConnell I mechanism for ferromagnetism proposed by Kollmar et al. and our previous calculations. Natural orbital analysis made it clear that the orbital overlap between SOMO on metals and SOMO on TCNE or TCNQ cations was nearly zero. These results indicated that orbital orthogonality was an important key factor for explaining the ferromagnetism of those systems.

The doubly Si-bridged ansa -tungstenocene, [W(η 5 -C 5 H 3 ) 2 (SiMe 2 ) 2 ], ( a -Si 2 Cp 2 W) is calculated to have singlet and triplet states of comparable energy, in contrast to other tungstenocenes which have triplet ground states. Therefore, on an SCF energy surface there is no barrier to formation of a sigma complex with methane, and formation of a methyl hydride is exo-energetic by −125 kJ mol −1 . Orbital analysis of the tungstenocenes shows that the singlet ground state is favoured by a ring conformation that stabilizes the 2b 1 orbital by back donation, and that a double ansa bridge promotes this ring conformation.

Density functional theory has been used to explore the energetics and bonding of the symmetric and unsymmetric isomeric sandwich complexes (η 5 -C 5 H 5 ) 2 M, (η 4 -C 4 H 4 )M(η 6 -C 6 H 6 ), and (η 3 -C 3 H 3 )M(η 7 -C 7 H 7 ) (M = Fe, Ru, Os). For each metal atom, the symmetric “5–5” metallocene was found to be the most stable isomer, with the “4–6” and “3–7” isomers ca. 40 and 80 kcal/mol higher in energy, respectively. Bonding analysis shows that (η 4 -C 4 H 4 )Fe(η 6 -C 6 H 6 ) is best considered as a (η 4 -C 4 H 4 )Fe fragment interacting with a C 6 H 6 ligand, although the interactions become less separable as the metal is changed to Ru and Os. Similarly, the dominant bonding in (η 3 -C 3 H 3 )M(η 7 -C 7 H 7 ) is that of a M(η 7 -C 7 H 7 ) perturbed by the interaction with a C 3 H 3 ligand.