Unsupported Lanthanide–Transition Metal Bonds: Ionic vs Polar Covalent?

Abstract

Lanthanide−transition metal complexes continue to be of interest, not only because of their synthetic challenge but also of their promising magnetic properties. Computational work examining the chemical bonding between lanthanides and transition metals in PyCp 2 Ln-TMCp(CO) 2 (DyPyCp 2 2− = [2,6-(CH 2 C 5 H 3 ) 2 C 5 H 3 N] 2− ) reveals strong Ln−TM dative bonds. Gasphase optimized geometries are in good agreement with experimental structures at the density functional theory (DFT) level with large-core pseudopotentials. From La to Lu, there is a small increase in the bond dissociation energy, as well as a decrease in Ln−Fe bond lengths. Energy decomposition analyses attribute this trend to an increase in the electrostatic contribution from the decreasing bond length and a modest increase in the orbital contribution. The natural bond orbital analysis clearly indicates that 3d 6 "lone pairs" in the [FeCp(CO) 2 ] − fragment act as a Lewis bases donating nearly 0.5 electron to Ln virtual orbitals of mainly d character. The interfragment bonding was also quantified by the quantum theory of atoms in molecules, which indicates that the Ln−Fe bond is more covalent than the Ca−Fe bond in the hypothetical CpCa-FeCp(CO) 2 but less covalent than the Zn−Fe bond in the hypothetical CpZn−FeCp(CO) 2 . Further comparisons suggest that to the [PyCp 2 Ln] + cation the [FeCp(CO) 2 ] − anion appears much like a halide. Overall, these Ln−TM dative bonds appear to have strong electrostatic contributions as well as significant orbital mixing and dispersion contributions.

Metal–metal bond in lanthanide single-molecule magnets

“…84,119,120 In 2021, Hall and fellows elucidated the nature of Ln–TM bonds in PyCp 2 Ln-TMCp(CO) 2 (PyCp 2 2− = [2,6-(CH 2 C 5 H 3 ) 2 C 5 H 3 N] 2− , TM = Fe, Ru) using multiple computational tools containing natural bond orbital (NBO) analysis, topological analysis, and energy decomposition analysis (EDA), showing that these special interactions were very similar to the Ln–I bonds and consist of predominant electrostatic contributions as well as significant orbital mixing and dispersion contributions. 121 On the other hand, concerning the vital role of Ln ions in SMMs field, inspecting the effects of Ln–TM bonds on the SMM behaviors is also an important line of inquiry. In 2018, Nippe et al reported the magnetization dynamics of the Ln–TM bonded compounds for the first time, PyCp 2 Dy–FeCp(CO) 2 and PyCp 2 Dy–RuCp(CO) 2 with Dy–Fe and Dy–Ru distances of 2.884(2) and 2.9508(5) Å, respectively (Fig.…”

Structure and Bonding Patterns in Heterometallic Organometallics with Short and Rare Ln-Pd Distances

“…When the fragments are computed as neutral species, the orbital interactions play the dominant role in the overall bonding energy -they constitute 66% of the attractive interaction, compared to 31% when the fragments are computed as charged species. The EDA analyses carried out by the group of Hall in a recent study 34 resulted in comparable differences in the relative contribution of the attractive orbital energy, depending on the charge of the fragments. In this study, the authors marked the difference between a situation with 26% of orbital interaction, analyzed as predominantly electrostatic, and another with 35 % of orbital interaction, analyzed as predominantly covalent.…”

“…29,33 As such, the use of this empirical metric as a guide for the bonding strength can be counterintuitive: reporting a short distance does not inform on the nature of the bonding, and the net definition of a lanthanide-transition metal bond can then be somewhat confusing in the literature. Based on these important remarks, Hall and co-workers recently studied a series of unsupported bimetallic complexes containing lanthanide and transition metal ions, 34 which were designed by the group of Nippe. 35 This study is an important addition to the discussion on the nature of metal-metal bonding and insists on the relative comparison along the series to validate the theoretical results.…”

Hidden Heterometallic Interaction Emerges from Resonant Inelastic X-ray Scattering in Luminescent Tb–Pt Molecules

“…Considerable efforts have thus been devoted to the formation of various intermetallic interactions. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Although highresolution X-ray diffraction analysis can provide insight into the electron density of bonds, 19 theoretical calculations are widely conducted for examining intermetallic interactions. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] In this study, we synthesized heterometallic Ln-Pt complexes:…”