La₂@C_s(17 490)‐C₇₆: A New Non‐IPR Dimetallic Metallofullerene Featuring Unexpectedly Weak Metal–Pentalene Interactions

Abstract

Although all the pure-carbon fullerene isomers above C60 reported to date comply with the isolated pentagon rule (IPR), non-IPR structures, which are expected to have different properties from those of IPR species, are obtainable either by exohedral modification or by endohedral atom doping. This report describes the isolation and characterization of a new endohedral metallofullerene (EMF), La2@C76, which has a non-IPR fullerene cage. The X-ray crystallographic result for the La2@C76/[Ni(II)(OEP)] (OEP=octaethylporphyrin) cocrystal unambiguously elucidated the C(s)(17,490)-C76 cage structure, which contains two adjacent pentagon pairs. Surprisingly, multiple metal sites were distinguished from the X-ray data, which implies dynamic behavior for the two La(3+) cations inside the cage. This dynamic behavior was also corroborated by variable-temperature (139)La NMR spectroscopy. This phenomenon conflicts with the widely accepted idea that the metal cations in non-IPR EMFs invariably coordinate strongly with the negatively charged fused-pentagon carbons, thereby providing new insights into modern coordination chemistry. Furthermore, our electrochemical and computational studies reveal that La2@C(s)(17,490)-C76 has a larger HOMO-LUMO gap than other dilanthanum-EMFs with IPR cage structures, such as La2@D(3h)(5)-C78 and La2@I(h)(7)-C80, which implies that IPR is no longer a strict rule for EMFs.

Strain Release of Fused Pentagons in Fullerene Cages by Chemical Functionalization

“…By using DFT computations in conjunction with statistical thermodynamic analysis, Zhao and co‐workers proposed that C 2 (13333)‐C 74 and C 2 (13295)‐C 74 bearing two pairs of DFPs were favored for La 2 @C 74 and Sc 2 @C 74 , as these had the highest thermodynamic stabilities with only small energy differences . In 2013, Akasaka and co‐workers isolated La 2 @C 76 and determined its molecular structure by single‐crystal X‐ray diffraction to be La 2 @ C s (17490)‐C 76 with two pairs of DFPs . Surprisingly, they found that the two La atoms resided close to the hexagonal rings rather than the fused pentagons (Figure f) and there were many disordered metal sites in the crystal structure.…”

Freisetzung der Spannung kondensierter Fünfringe des Fullerenkäfigs durch chemische Funktionalisierung

“…Der Fall von La 2 @C s (17490)-C 76 , mit einer schwächeren Wechselwirkung zwischen den eingeschlossenen Metallatomen und den kondensierten Fünfringen, lässt darauf schließen, dass fürd ie Stabilisierung endohedraler Nicht-IPR-Fullerene die Komplexierung der Metallatome mit den kondensierten Fünfringen nicht so wichtig wie der Ladungstransfer vom Metall zum Kohlenstoffkäfig ist. [19]…”

“…Vondaanwurden Dutzende von endohedralen Nicht-IPR-Fullerenen experimentell isoliert, wobei das Merkmal, nicht der IPR zu folgen, mittels Einkristall-Rçntgenbeugung eindeutig festgestellt wurde. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] Somit wird demonstriert, dass die endohedrale Funktionalisierung des Fullerenkäfigs eine wirksame Methode zur Freisetzung der Spannung kondensierter Fünfringe ist.…”

The inner-induced effects of YCN in C76 on the structures and nonlinear optical properties

“…EMFs formed have now been revealed to entrap atoms, or clusters into the cage. The number of encaged atoms inside the fullerene cage, such as Ca@C 60 [37], Li@C 60 [38][39][40], M@C 74 (M = La, Ca, Ba) [41], Sc 2 @C 66 [42], M@C 76 (M = Yb, Ca, Sr, Ba) [43,44], Sm@C 76 [45] La 2 @C 76 , [46] Na@C 60 C 60 @F [30], and so on. The cluster EMFs, containing two or more metal atoms and non-metallic atoms inside the fullerene cages, such as MCN@C 76 (Sc and Y) [47], Sc 3 N@C 78 [48], M 3 N@I h -C 80 (M = Y and Gd) [49], Sc 4 O 2 @C 80 [50], YCN@C 82 [51], Sc 2 C 2 @C 82 [52], Sc 3 N@C 82 [53].…”

“…C 76 fullerenes are currently of considerable interest, much effort has been devoted to research the novel derivatives of fullerenes with metal atom(s) or clusters encapsulated inside [43][44][45][46][58][59][60]. Among classical fullerene isomers of C 76 , our present work has been mainly focused on C 2v (19138)-C 76 , C 1 (17459)-C 76 , C 2 (17646)-C 76 , and C 1 (17894)-C 76 with a pair of adjacent pentagons, which belongs to the nonisolated pentagon rule (non-IPR).…”