Ab Initio Study of Metal−Ring Bonding in the Bis(η⁶-benzene)lanthanide and -actinide Complexes M(C₆H₆)₂ (M = La, Ce, Nd, Gd, Tb, Lu, Th, U)

Abstract

The zerovalent bis(η6-benzene) f-metal sandwich complexes M(C6H6)2 (M = La, Ce, Nd, Gd, Tb, Lu, Th, U) were investigated with state-of-the-art quantum chemical ab initio approaches taking into account the effects of electron correlation and relativity. Ground state assignments, optimized metal−ring distances, symmetric metal−ring stretching frequencies, and metal−ring bonding energies are reported. The effects of ring substitution on the metal−ring binding energies are discussed. The complexes of Th and U are predicted to be at least as stable as the corresponding lanthanide systems and form possible synthetic targets. Whereas the lanthanide systems have a 4f n ground state configuration (n = 1, 3 for Ce, Nd), the corresponding actinide compounds should possess, as a consequence of stronger relativistic effects, a 5f n -1 ground state configuration, with a possible strong admixture of 5f n -1 (n = 1, 3 for Th, U). The back-donation from the occupied metal d± 2 to the empty π orbitals of the benzene ligands is found to be the dominant bonding interaction. Whereas the lanthanide 4f orbitals are essentially localized on the metals and chemically inactive, the actinide 5f shell is partially delocalized and its f± 2 components may also take part in the back-donation.

Titanium as a Potential Addition for High-Capacity Hydrogen Storage Medium

“…The structure of the C 6 H 6 -Ti complex has been theoretically [20][21][22][23][24][25][26][27] and experimentally [28] studied on the basis of DFT calculations and laser evaporation methods. Experimental evidence indicates the ground state to be a triplet in a planar C 6v configuration.…”

“…Our OLYP calculations predict a triplet-C 2v configuration as ground state of the C 6 H 6 -Ti compound, with the quintet-C 6v (e 2 ) 2 (da 1 ) 1 (4s) 1 and triplet-C 6v (e 2 ) 3 (da 1 ) 1 (4s) 0 configurations lying higher in energy by 0.372 and 0.242 eV, respectively. Previously, both triplet-C 2v [20,24,26] and quintet-C 6v [21-23, 25, 27, 28] states have been theoretically predicted as possible ground states. However, a quintet-C 6v ground state was predicted only by the B3LYP method, and previous studies on the reaction products formed between group 5 transition metals (V, Nb, Ta) and benzene revealed the B3LYP method to calculate the correct ground state only for the C 6 H 6 -Nb complex [29].…”

σ-Donor versus η6-π-Arene Interactions in Monomeric Europium(II) and Ytterbium(II) Thiolates − An Experimental and Computational Study

“…[38,39] To gain more insight into the Eu 2ϩ Ϫ or Yb 2ϩ Ϫarene interactions present in 4a and 4b, ab initio calculations on suitable model systems were performed. Quasi-relativistic pseudo-potentials of the Stuttgart/Bonn group were employed for atoms heavier than sulfur.…”

Electronic states of neutral and cationic bis(benzene) titanium and vanadium sandwich complexes studied by pulsed field ionization electron spectroscopy

“…The prediction of the singlet ground state for the neutral Ti-bz 2 complex is consistent with previous DFT or ab initio calculations. [23][24][25][26][27][28][29] For the ionized complex, we have located a 4 A 1g state in D 6h symmetry and a 2 B 1g state in a slightly puckered D 2h symmetry. The 2 B 1g state is 1484 cm −1 above the 4 A 1g state.…”

“…The determination of the low spin electronic states of these sandwich complexes also confirms the previously theoretical predictions that the metal-ligand backdonation is the major binding mechanism in these early transition metal complexes. 22,27 Ideally, these molecules have a sixfold principal rotational axis and are in D 6h symmetry. Under this symmetry, metal atomic 3d orbitals span three irreducible representations, which are energetically ordered as 38 Electron occupation of the 3de 2g ͑␦͒ orbitals maximizes the electron backdonation into the lowest unoccupied * orbitals on the benzene rings and increases the metal-ligand interaction.…”