Favorite Orientation of the Carbon Cage and a Unique Two-Dimensional-Layered Packing Model in the Cocrystals of Nd@C₈₂(I,II) Isomers with Decapyrrylcorannulene

Abstract

To date, the experimental studies on Nd-based metallofullerenes are only limited to spectroscopic characterizations. In this work, the molecular structures of Nd@C82(I,II) isomers, including the isomeric symmetry of the C cage and the position of endohedral Nd atom, as well as their unique two-dimensional (2D)-layered crystallographic packing structures were initially and unambiguously elucidated, based on the X-ray structural analyses of the cocrystals of Nd@C82(I) or Nd@C82(II) with cocrystallizing agent decapyrrylcorannulene (DPC). In the V-shaped unit cell, the endohedral Nd atom prefers a site as far away from the DPC molecules as possible because of the unevenly distributed charge on the C cage mainly related to the charge transfers from the endohedral Nd atom, cocrystallizing agent DPC, and solvent toluene molecules to the C82 cage. Apart from charge transfers, multiple C–H···π intermolecular interactions are also confirmed to play important roles both for the orientation of the C cage correlated with the preferential sites of the endohedral Nd atom and for the 2D-layered packing structures within the cocrystals. Density functional theory computations offered theoretical support for the molecular structures of Nd@C82(I,II) isomers, the valence of the endohedral Nd atom (between II+ and III+), and the global ground state, i.e., the Nd@C 2v (9)-C82 isomer in the quintet state.

Monometallic Endohedral Azafullerene

“…The La@C 81 N molecule is surrounded by two DPC molecules, which construct a V-shape clam with an angle of 64.7°. The nearest DPC-cage distances are 3.293(13) and 3.441(16) Å, respectively, comparable to those of the previously reported cocrystals consisting of DPCs and other monometallic EMFs, such as Nd@C 2v (9)-C 82 and Nd@C s (6)-C 82 , 29 disclosing the π−π interactions between the two DPC molecules and LaC 81 N.…”

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

“…However, on the basis of the crystallographic results for U@ C s (6)-C 82 and U@ C s (15)-C 84 , we wondered if the encapsulated metal ions are always located on symmetry planes of the fullerene cages, as long as the fullerene cages possess mirror planes. In order to gain a more fundamental understanding of metal–cage interactions, we reanalyzed the structures of published mono-metallofullerenes that have been reported from X-ray diffraction studies. − Except for M@ I h -C 60 (CF 3 ) 5 (M = La and Gd), La@ D 5 h -C 70 (CF 3 ) 3 , and La@ C 2 (10612)-C 72 (C 6 H 3 Cl 2 ), which were characterized in the form of derivatives, the crystallographically characterized mono-metallofullerenes with 30 different kinds of pristine cages are shown in Figure , among which 15 possess cages with symmetry planes, and the other 15 do not. Notably, only one metal was selected to show when various metals were encapsulated in the same cage.…”

“…The development of cocrystallization methods using metal porphyrins, which improve the crystallinity and inhibit the rotation of the fullerene cages, makes the structural studies of EMFs much easier and more accurate . Up to now, mono-metallofullerenes containing various metal elements, including alkaline-earths, , rare-earths, − and actinides, − have been crystallographically characterized.…”

“…On the other hand, it is challenging to develop general rules governing the metal–cage interactions for mono-metallofullerenes because the metal positions change depending on the fullerene cage. For example, for M@ C 2 v (9)-C 82 (M = lanthanide and U), − the metal is generally situated on the C 2 axis, while for M@ C 2 v (3)-C 80 (M = Sm, Yb, and Eu) − with the same cage symmetry as M@ C 2 v (9)-C 82 , the metal is not on the C 2 axis. Trying to understand the reasons for these observations should provide fundamental insights about the nature of the metal–cage interactions and the formation of the EMFs.…”

Capturing the Missing Carbon Cage Isomer of C84 via Mutual Stabilization of a Triangular Monometallic Cyanide Cluster

“…Molecular structures of YCN@C 84 , DyCN@C 84 (I), DyCN@C 84 (II), and TbCN@C 84 were determined unambiguously by single-crystal X-ray diffraction based on high-quality cocrystals obtained by using different hosts (see Table S2 for detailed crystallographic data). TbCN@C 84 was cocrystallized with Ni II (OEP) (OEP = octaethylporphyrin), which is commonly used as a host in the X-ray crystallographic study of endohedral metallofullerenes, ,,− while YCN@C 84 , DyCN@C 84 (I), and DyCN@C 84 (II) cocrystallized with a decapyrrylcorannulene (DPC) host developed by us recently. − Figure a–d illustrate the relative orientations of YCN@ C 2 (13)-C 84 , DyCN@ C 2 (13)-C 84 , TbCN@ C 2 (13)-C 84 , and DyCN@ C 2 v (17)-C 84 within the corresponding YCN@ C 2 (13)-C 84 ·2DPC, DyCN@ C 2 (13)-C 84 ·2DPC, TbCN@ C 2 (13)-C 84 ·Ni II (OEP), and DyCN@ C 2 v (17)-C 84 ·2DPC cocrystals, in which only one orientation of the fullerene cage together with the major site of the MCN cluster is given for clarity. Interestingly, when the DPC host is used, two DPC molecules embrace one fullerene molecule of YCN@ C 2 (13)-C 84 /DyCN@ C 2 (13)-C 84 /DyCN@ C 2 v (17)-C 84 with a V-shape geometry, whereas the stoichiometric ratio changes to 1:1 for the Ni II (OEP) host in the case of the TbCN@ C 2 (13)-C 84 ·Ni II (OEP) cocrystal.…”