From π Bonds without σ Bonds to the Longest Metal–Metal Bond Ever: A Survey on Actinide–Actinide Bonding in Fullerenes

Abstract

Actinide–actinide bonds are rare. Only a few experimental systems with An–An bonds have been described so far. Recent experimental characterization of the U2@I h (7)-C80 (J. Am. Chem. Soc. 2018, 140, 3907) system with one-electron two-center (OETC) U–U bonds as was predicted by some of us (Phys. Chem. Chem. Phys. 2015, 17, 24182) encourages the search for more examples of actinide–actinide bonding in fullerene cages. Here, we investigate actinide–actinide bonding in An2@D 5h (1)-C70, An2@I h (7)-C80, and An2@D 5h (1)-C90 (An = Ac–Cm) endohedral metallofullerenes (EMFs). Using different methods of the chemical bonding analysis, we show that most of the studied An2@C70 and An2@C80 systems feature one or more one-electron two-center actinide–actinide bonds. Unique bonding patterns are revealed in plutonium EMFs. The Pu2@I h (7)-C80 features two OETC Pu–Pu π bonds without any evidence of a corresponding σ bond. In the Pu2@D 5h (1)-C90 with r Pu–Pu = 5.9 Å, theory predicts the longest metal–metal bond ever described. Predicted systems are thermodynamically stable and should be, in principle, experimentally accessible, though radioactivity of studied metals may be a serious obstacle.

Atomically Precise Insights into Metal–Metal Bonds Using Comparable Endo-Units of Sc 2 and Sc 2 C 2

“…However, only a few cases have been found experimentally or theoretically after considerable efforts to explore endo-metal-metal bonds in fullerene cages. [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] An unexpected challenge in determining endo-metal-metal bonding in fullerene cages by X-ray crystallography is posed by severe disorder in the crystal structures, especially for metallic endo-clusters, and there can be up to tens of disordered sites when determining endo-metal atoms in a fullerene cage. Therefore, searching for an example system with less metallic disorder is the key to precisely elucidating the nature of endo-metal-metal bonds.…”

Covalency in actinide(iv) hexachlorides in relation to the chlorine K-edge X-ray absorption structure

“…Elucidation of the chemical bonding in lanthanide (Ln) and actinide (An) systems is presently the goal of many joint experimental and theoretical efforts. Such knowledge is of paramount importance for a wide range of applications, including the development of Ln and An-based single-molecule magnets, [1][2][3][4][5][6] metal-organic frameworks, [7][8][9][10][11] endohedral metallofullerenes, [12][13][14][15][16][17] nanoparticles for industrial catalytic reactions and biomedicine, 18 and the design of chelating ligands for f-element separation. [19][20][21][22][23] Rational design of new f-element materials and separation ligands requires knowledge of the ionic vs. covalent behavior of the Ln 4f/5f and An 5f/6d shells.…”

X-ray absorption spectra of f-element complexes: insight from relativistic multiconfigurational wavefunction theory

“…Research of the physico-chemical properties of compounds containing lanthanide (Ln) or actinide (An) elements is rapidly evolving in response to the urgent need for exploring the extent of f-shell chemical bonding in a variety of applications. [1][2][3][4][5][6][7][8][9][10][11] With radially compact 4f orbitals, Ln chemistry is dominated by the +III oxidation state, with +II and +IV being important variations. [12][13][14][15] Prior to Cm, actinide chemistry is characterized by a large variety of oxidation states.…”