Isolation and Crystallographic Characterization of Lu₃N@C_2n (2n=80–88): Cage Selection by Cluster Size

Abstract

The small Sc N cluster has only been found in such small cages as C (2n=68, 78, 80, 82), whereas the large M N (M=Y, Gd, Tb, Tm) clusters choose those larger cages C (2n=82-88). Herein, concrete experimental evidence is presented to establish the size effect of the internal metallic cluster on selecting the outer cage of endohedral metallofullerenes (EMFs) by using a medium-sized metal, lutetium, which possesses an ionic radius between Sc and Gd. A series of lutetium-containing EMFs have been obtained and their structures are unambiguously determined as Lu N@I (7)-C , Lu N@D (6)-C , Lu N@C (9)-C , Lu N@C (51365)-C , Lu N@D (17)-C , and Lu N@D (35)-C by single-crystal X-ray diffraction crystallography. It was confirmed that the encaged Lu N cluster always adopts a planar geometry in Lu N@C isomers to ensure substantial metal-cage/metal-nitrogen interactions. As a result, the Lu N cluster selects the C (9)-C cage, which also encapsulates Sc N, instead of the C (39663)-C cage which is more suitable for M N (M=Y, Gd, Tb, Tm). However, different from Sc N, Lu N can also template the C cages which are absent for Sc N-containing EMFs, confirming clearly the size effect of the internal cluster on selecting the outer cage.

Interconversions between Uranium Mono-metallofullerenes: Mechanistic Implications and Role of Asymmetric Cages

“…Notably, the fullerene cages for U@C 84 and U@C 86 (I) are not the same IPR isomers found for the previously reported Sm@ D 3 d (19)-C 84 , Sm@ C 2 (13)-C 84 , Eu@ D 3 d (19)-C 84 , Eu@ C 2 (13)-C 84 , Eu@ C 2 (11)-C 84 , Yb@ C 2 (13)-C 84 , Lu 2 @ C 2 v (7)-C 84 , Lu 2 @ D 2 d (23)-C 84 , Sc 2 C 2 @ D 2 d (23)-C 84 , Eu@ C 1 (7)-C 86 , Lu 2 @ C s (8)-C 86 , Lu 2 @ C 2 v (9)-C 86 , Lu 2 C 2 @ C 2 v (9)-C 86 , Sc 2 C 2 @ C 2 v (9)-C 86 , Gd 3 N@ D 3 (19)-C 86 , Tb 3 N@ D 3 (19)-C 86 , and Lu 3 N@ D 3 (19)-C 86 . Analysis of cage connectivity identified U@C 84 as U@ D 2 (21)-C 84 and U@C 86 (I) as U@ C s (15)-C 86 , the same C s (15)-C 86 was only reported for Lu 2 @C s (15)-C 86 previously .…”

“…Accordingly, the intact fullerene cage is generated by combining one half of the cage with the mirror image of the Notably, the fullerene cages for U@C 84 and U@C 86 (I) are not the same IPR isomers found for the previously reported Sm@D 3d (19)-C 84 , 24 Sm@C 2 (13)-C 84 , 24 Eu@D 3d (19)-C 84 , 25 Eu@C 2 (13)-C 84 , 14 Eu@C 2 (11)-C 84 , 14 Yb@C 2 (13)-C 84 , 26 Lu 2 @C 2v (7)-C 84 , 27 Lu 2 @D 2d (23)-C 84 , 28 Sc 2 C 2 @D 2d (23)-C 84 , 29 Eu@C 1 (7)-C 86 , 14 Lu 2 @C s (8)-C 86 , 27 Lu 2 @C 2v (9)-C 86 , 28 Lu 2 C 2 @C 2v (9)-C 86 , 27 Sc 2 C 2 @C 2v (9)-C 86 , 19 Gd 3 N@D 3 (19)-C 86 , 30 Tb 3 N@D 3 (19)-C 86 , 31 and Lu 3 N@D 3 (19)-C 86 . 32 Analysis of cage connectivity identified U@C 84 as U@D 2 (21)-C 84 and U@C 86 (I) as U@C s (15)-C 86 , the same C s (15)-C 86 was only reported for Lu 2 @C s (15)-C 86 previously. 27 It is important to note that D 2 (21)-C 84 is a totally new chiral cage, for which we observe the two enantiomers (cage 1 and cage 1A), see Figure S4.…”

Endohedral Metallofullerenes: New Structures and Unseen Phenomena

“…Until recently, crystallographic results and DFT calculations confirmed that the M 3 N@C 80–88 (M=Lu, Er) isomers also accommodate a planar M 3 N cluster inside (Figure ). Specifically, the M−N distances of the major M 3 N sites in M 3 N@C 80–88 (M=Lu, Er) isomers increase with cage expansion owing to the strong metal–cage interactions to maintain the planar geometry of the M 3 N unit (Figure ).…”

“… The M–N distances of the major M 3 N site as a function of the cage size in (a) Lu 3 N@C 80–88 and (b) Er 3 N@C 80–88 series. (Values for Er 3 N@C 86 were obtained from theory).…”

“…To date, a collection of EMFs containing one to three pure metal atoms, which are called mono‐, di‐, and tri‐EMFs, respectively, has been obtained and structurally characterized . In addition, various metallic clusters, such as metal carbides, nitrides, oxides, sulfides, and even cyanides, have also been trapped inside fullerene cages to form the corresponding cluster‐EMFs. More meaningfully, the variability of the encapsulated species endows the EMFs with multifunctional properties and potential applications in optoelectronics, or as magnetic resonance imaging contrast agents, single‐molecule magnets, electron‐spin quantum computing units, and so forth.…”