Fused-pentagons results in an increase of local steric strain according to the isolated pentagon rule (IPR), and for all reported non-IPR clusterfullerenes multiple (two or three) metals are required to stabilizet he strained fused-pentagons, making it difficult to access the single-atom properties.Herein, we report the syntheses and isolations of novel non-IPR mononuclear clusterfullerenes MNC@C 76 (M = Tb,Y ), in which one pair of strained fused-pentagon is stabilized by amononuclear cluster.The molecular structures of MNC@C 76 (M = Tb,Y)were determined unambiguously by single-crystal X-ray diffraction, featuring an on-IPR C 2v (19138)-C 76 cage entrapping an early linear MNC cluster,w hichi sr emarkably different from the triangular MNC cluster within the reported analogous clusterfullerenes based on IPR-obeying C 82 cages. The TbNC@C 76 molecule is found to be afield-induced singlemolecule magnet (SMM).
Fullerenesareclosedcarboncageswithhollowinteriors,andsuch unique structures bring about intriguing physical and chemical properties.[1] Most fullerenes isolated during the past three decades are based on classical carbon cages composed of hexagons and pentagons only, [1,2] forw hich the stability is generally determined by the isolated pentagon rule (IPR) proposed by Kroto in the 1980s.[3] According to IPR, fusedpentagons result in an increase of local steric strain of ac arbon cage,t hus destabilizing the fullerene. [3,4] Stabilization of the strained fused-pentagon within an on-IPR fullerene cage has been fulfilled by either endohedral or exohedral derivatization.[4] In particular,f or endohedral fullerenes which are as pecial class of fullerene with an atom, ion, or cluster entrapped in the interior of carbon cage, [5] the strong coordination of the entrapped metal ion(s) with the fused-pentagon gives rise to an intramolecular electron transfer and consequently stabilization of the non-IPR endohedral fullerene. [4][5][6] Most of the non-IPR endohedral fullerenes reported to date are based on clusterfullerenes [7] owing to the feasibility of entrapping multiple metals in diverse forms of metal clusters,s uch as Sc 3 N@C 68 , [6a,b] Gd 3 N@C 2n (2n = 78, 82, 84), [6c-e] LaSc 2 N@C 80 , [6f] and Sc 2 S@C 72 .[6g] Noteworthy,f or these reported non-IPR clusterfullerenes,multiple (two or three) metal ions are required to stabilize simultaneously the charged metal clusters and the fused-pentagons.H ence,i ti sd esirable to synthesize novel non-IPR endohedral fullerenes containing mononuclear metal clusters.Clusterfullerenes have been recently recognized as single molecule magnets (SMMs) with potential applications in spintronics,q uantum computing,a nd high-density storage devices. [8,9] To date only af ew endohedral fullerene SMMs have been reported, including Ln x Sc 3Àx N@C 80 (Ln = Dy,H o, x = 1, 2) [9a-d] and Dy 2 TiC@C 80 , [9e] which are all based on an I h -C 80 cage entrapping multiple rare-earth-metal ions that are fixed as atriangle along with the central non-magnetic ion (N or C)...
