Characterization of a strong covalent Th3+–Th3+ bond inside an Ih(7)-C80 fullerene cage

Abstract

The nature of the actinide-actinide bonds is of fundamental importance to understand the electronic structure of the 5f elements. It has attracted considerable theoretical attention, but little is known experimentally as the synthesis of these chemical bonds remains extremely challenging. Herein, we report a strong covalent Th-Th bond formed between two rarely accessible Th3+ ions, stabilized inside a fullerene cage nanocontainer as Th2@Ih(7)-C80. This compound is synthesized using the arc-discharge method and fully characterized using several techniques. The single-crystal X-Ray diffraction analysis determines that the two Th atoms are separated by 3.816 Å. Both experimental and quantum-chemical results show that the two Th atoms have formal charges of +3 and confirm the presence of a strong covalent Th-Th bond inside Ih(7)-C80. Moreover, density functional theory and ab initio multireference calculations suggest that the overlap between the 7s/6d hybrid thorium orbitals is so large that the bond still exists at Th-Th separations larger than 6 Å. This work demonstrates the authenticity of covalent actinide metal-metal bonds in a stable compound and deepens our fundamental understanding of f element metal bonds.

Electrophilic Trifluoromethylation of Dimetallofullerene Anions en Route to Air-Stable Single-Molecule Magnets with High Blocking Temperature of Magnetization

“…Similar preferential orientation of endohedral metal ions toward N−Ni−N leading to a considerable degree of the crystallographic order was reported for NiOEP cocrystals with nitride clusterfullerenes M 3 N@C 80 . 79,90−94 Regioselective addition of CF 3 group to the [5,6,6] carbon of Tb 2 @C 80 is in line with earlier studies on addition chemistry of dimetallofullerenes M 2 @C 80 . Highly symmetric C 80 -I h cage has only two types of carbon atoms, 60 C- [5,6,6] atoms at pentagon/hexagon/hexagon junction and 20 C- [6,6,6] atoms at triple hexagon junctions.…”

“…79,90−94 Regioselective addition of CF 3 group to the [5,6,6] carbon of Tb 2 @C 80 is in line with earlier studies on addition chemistry of dimetallofullerenes M 2 @C 80 . Highly symmetric C 80 -I h cage has only two types of carbon atoms, 60 C- [5,6,6] atoms at pentagon/hexagon/hexagon junction and 20 C- [6,6,6] atoms at triple hexagon junctions. All structurally characterized M 2 @ C 80 (R) compounds reported so far (here R is a radical group attached to the fullerene via single C−C bond, such as trifluoromethyl CF 3 , benzyl CH 2 Ph, 7,82 or triazinyl C 3 N 3 Ph 2 83 ) have their exohedral group attached to the [5,6,6] site.…”

“…Single-Crystal and DFT Analysis. Molecular structure of {Tb 2 }-CF 3 with I h (7)-C 80 cage isomer and CF 3 group attached to the pentagon/hexagon/hexagon junction (aka [5,6,6] position) was unambiguously determined by single-crystal Xray diffraction (SC-XRD). Single crystals with composition 2Tb 2 @C 80 (CF 3 )•4NiOEP•xC 6 H 6 •yC 7 H 8 were obtained by cocrystallization of {Tb 2 }-CF 3 in toluene with nickel octaethylporphyrin (NiOEP) in benzene.…”

“…7,8,16−20 In di-EMFs of early lanthanides, metal dimers tend to transfer all of their six valence electrons to the carbon cage, ensuring its closed-shell electronic structure with (M 2 ) 6+ @C 80 6− charge distribution. But in M 2 @C 80 molecules with heavy lanthanides (M = Gd−Er), the metal dimer keeps one valence electron on the metal−metal bonding orbital, resulting in the formal charge distribution of (M 2 ) 5+ @ C 80 5− and a fullerene cage deficient of one electron to complete the closed-shell configuration. These di-EMFs are not soluble in nonpolar solvents that are commonly used to dissolve fullerenes (CS 2 or toluene and other aromatic solvents) but can be extracted from the soot by boiling dimethylformamide (DMF) in the form of monoanions M 2 @C 80 − with (M 2 ) 5+ @ C 80 6− charge distribution (reduction agent is presumably an amine formed in the course of the partial thermal decomposition of DMF).…”

Crystallographic Characterization of U@C2n (2n = 82–86): Insights about Metal–Cage Interactions for Mono-metallofullerenes

“…To better understand the interaction between the uranium ions and the carbon cages and the role of symmetry in the location of the U inside the fullerenes, we have explored the lowest-energy uranium sites for the four new monometallic EMFs displayed in Figure . U and also Th tend to formally possess oxidation states of 4+ or 3+ depending on whether the fullerene cage encapsulates one − or two , metals. For the smallest fullerene, U@ C s (6)-C 82 , the three lowest-energy positions for the U ion are located on the plane of symmetry of the carbon cage, the most favored one being that where U interacts with a phenalene (site A in Figure a).…”