Covalency in f-element complexes

Reversible Sigma C–C Bond Formation Between Phenanthroline Ligands Activated by (C5Me5)2Yb

“…Since the overlap between the ligand orbitals and the Yb 5d orbitals is anticipated to be significantly larger than the overlap with the Yb 4f orbitals, whether the ground state is a singlet or triplet depends in large part on the energies of the ligand orbitals. 40 If the half-occupied ligand orbital is close in energy to the 4f-orbitals and has the proper symmetry to overlap with the lone half-filled Yb 4f-orbital, the singlet state is likely to be lowest in energy. However, if the half-occupied ligand orbital is not close in energy to the 4f orbitals or does not have the proper symmetry to overlap with the half-occupied Yb 4f orbital, the interaction between the half-occupied ligand orbital and the Yb 5d orbitals will be 31 stronger, and the triplet state will be stabilized.…”

A Macrocyclic Chelator That Selectively Binds Ln4+ over Ln3+ by a Factor of 1029

“…It is important to note that the energetic stabilization gained due to 4f covalency is proportional to the overlap between 4f and ligand-based orbitals. 173,175 Hence, because the radial extension of the 4f orbitals is very small, [176][177][178][179] increasing 4f covalency by decreasing the energy separation of the metal and ligand orbitals may act to weaken the bond overall by decreasing the amount of ionic character in the ground state. This work also illustrates that thermodynamic, spectroscopic, and theoretical studies of tetravalent cerium molecules is a fruitful area for research.…”

“…[173][174][175] In this model, the 4f orbitals for Figure 13. Qualitative molecular orbital diagram depicting the interaction between lanthanide 4f or actinide 5f orbitals and ligand 2p or 3p orbitals to form a metal-ligand bond.…”

Group 3 metal stilbene complexes: synthesis, reactivity, and electronic structure studies

“…For example, rare-earths show similar chemical reactivity within the series despite a different number of f electrons, because these electrons are shielded. 1,2 On the other hand, actinides, of which uranium and thorium are studied the most, show involvement of f electrons in bonding, [3][4][5][6] and uranium has several oxidation states accessible. 7 The differences between lanthanides and early actinides are most striking in their organometallic chemistry.…”

“…7 The differences between lanthanides and early actinides are most striking in their organometallic chemistry. 4,5 Group 3 metals (scandium, yttrium, lanthanum, and lutetium) usually show chemistry representative of all rare earths and their compounds are easier to characterize because of their diamagnetic nature. 8,9 Their classification with lanthanides rather than with transition metals is supported by the fact that, with few exceptions, 9 their complexes contain the metal in the +3 oxidation state, while transition metals display multiple oxidation states.…”