The Unanticipated Dimerization of Ce@C_2v(9)‐C₈₂ upon Co‐crystallization with Ni(octaethylporphyrin) and Comparison with Monomeric M@C_2v(9)‐C₈₂ (M = La, Sc, and Y)

Abstract

We report that Ce@C (9)-C forms a centrosymmetric dimer when co-crystallized with Ni(OEP) (OEP = octaethylporphyrin dianion). The crystal structure of {Ce@C (9)-C } ⋅2[Ni(OEP)]⋅4 C H shows that a new C-C bond with a bond length of 1.605(5) Å connects the two cages. The high spin density of the singly occupied molecular orbital (SOMO) on the cage and the pyramidalization of the cage are factors that favor dimerization. In contrast, the treatment of Ni(OEP) with M@C (9)-C (M = La, Sc, and Y) results in crystallization of monomeric endohedral fullerenes. A systematic comparison of the X-ray structures of M@C (9)-C (M = Sc, Y, La, Ce, Gd, Yb, and Sm) reveals that the major metal site in each case is located at an off-center position adjacent to a hexagonal ring along the C axis of the C (9)-C cage. DFT calculations at the M06-2X level revealed that the positions of the metal centers in these metallofullerenes M@C (9)-C (M = Sc, Y, and Ce), as determined by single-crystal X-ray structure studies, correspond to an energy minimum for each compound.

Endohedral Metallofullerenes: New Structures and Unseen Phenomena

“…Unexpectedly, subsequent reports demonstrated that a regioselective dimerization can be observed in the crystalline states of Y@ C s (6)‐C 82 (Figure a) and Er@ C s (6)‐C 82 (Figure b) upon co‐crystallization with Ni(OEP) (OEP is the dianion of octaethylporphyrin) in which two fullerene cages are connected by a C−C single bond. Another dimer of pristine EMFs was also observed in the cerium‐containing mono‐EMF co‐crystals (Figure c), [Ce@ C 2 v (9)‐C 82 ] 2 ⋅ 2[Ni(OEP)] . However, no dimerization occurs for M@ C 2 v (9)‐C 82 (M=Y, Er, Sc, La) under the same crystallization conditions .…”

“…Another dimer of pristine EMFs was also observed in the cerium‐containing mono‐EMF co‐crystals (Figure c), [Ce@ C 2 v (9)‐C 82 ] 2 ⋅ 2[Ni(OEP)] . However, no dimerization occurs for M@ C 2 v (9)‐C 82 (M=Y, Er, Sc, La) under the same crystallization conditions . Density functional theory (DFT) calculations on Y@ C s (6)‐C 82 and Er@ C s (6)‐C 82 reveal that the high spin density caused by the stable displacement of metal atoms in the C s (6)‐C 82 cage should be responsible for the regioselective dimer formation .…”

“…Density functional theory (DFT) calculations on Y@ C s (6)‐C 82 and Er@ C s (6)‐C 82 reveal that the high spin density caused by the stable displacement of metal atoms in the C s (6)‐C 82 cage should be responsible for the regioselective dimer formation . For the origin of dimerization of Ce@ C 2 v (9)‐C 82 , DFT calculations proposed that the predominate spin density and pyramidalization of the unique cage atom are the key factors that favor the dimerization . Note that in these three systems, their major metal centers are all positioned close to the porphyrin molecules in the dimers, whereas the corresponding dimerization sites are all far away from the respective inner metal atoms (Figure ), indicating that the metal location may exert important influences on determining the site of dimerization.…”

Robust metal‐pentagon interactions in the Th‐based endohedral metallofullerenes revealed by DFT calculations

“…Our optimized geometry is very similar to the single crystal structure of Th@C 3v (8)‐C 82 , and both of them show an metal position close to the three pentagons of THJ fragment (Scheme ). In the conventional M@C 2v (9)‐C 82 (M = Sc, Y, La, Ce, Eu, Gd, etc), the metals are all perfectly located under a hexagonal ring on the C 2 axis with the C 2v cage symmetry intact. In sharp contrast, Th@C 2v (9)‐C 82 shows an off‐axis metal position with the Th atom situated close to three THJ pentagons, and the molecular symmetry reduces to C s accordingly.…”

Molecular Structure and Magnetic and Optical Properties of Endometallonitridofullerene Sc3N@Ih‐C80 in Neutral, Radical Anion, and Dimeric Anionic Forms

“…For example, the neutral singly bonded (C 59 N) 2 dimer, isoelectronic with the (C 60 − ) 2 dimer, begins to dissociate only above 500 K . Several examples of neutral dimers of paramagnetic monometallofullerenes have been studied in the solid phase, but their thermal stability has not been investigated –. In contrast to empty fullerenes, endometallonitridofullerenes experience intrinsic charge transfer from the M 3 N cluster to the fullerene cage, thereby increasing the negative charge on the cage and a large positive charge appears on the scandium atoms.…”