X-ray structures of Sc2C2@C2n (n = 40-42): in-depth understanding of the core-shell interplay in carbide cluster metallofullerenes

X-ray analyses of the cocrystals of a series of carbide cluster metallofullerenes Sc(2)C(2)@C(2n) (n = 40-42) with cobalt(II) octaethylporphyrin present new insights into the molecular structures and cluster-cage interactions of these less-explored species. Along with the unambiguous identification of the cage structures for the three isomers of Sc(2)C(2)@C(2v)(5)-C(80), Sc(2)C(2)@C(3v)(8)-C(82), and Sc(2)C(2)@D(2d)(23)-C(84), a clear correlation between the cluster strain and cage size is observed in this series: Sc-Sc distances and dihedral angles of the bent cluster increase along with cage expansion, indicating that the bending strain within the cluster makes it pursue a planar structure to the greatest degree possible. However, the C-C distances within Sc(2)C(2) remain unchanged when the cage expands, perhaps because of the unusual bent structure of the cluster, preventing contact between the cage and the C(2) unit. Moreover, analyses revealed that larger cages provide more space for the cluster to rotate. The preferential formation of cluster endohedral metallofullerenes for scandium might be associated with its small ionic radius and the strong coordination ability as well.     

Sc2C2@C80 rather than Sc2@C82: templated formation of unexpected C2v(5)-C80 and temperature-dependent dynamic motion of internal Sc2C2 cluster

Unambiguous X-ray crystallographic results of the carbene adduct of Sc(2)C(82) reveal a new carbide cluster metallofullerene with the unexpected C(2v)(5)-C(80) cage, that is, Sc(2)C(2)@C(2v)(5)-C(80). More interestingly, DFT calculations and NMR results disclose that the dynamic motion of the internal Sc(2)C(2) cluster depends strongly on temperature. At 293 K, the cluster is fixed inside the cage with two nonequivalent Sc atoms on the mirror plane, thereby leading to C(s) symmetry of the whole molecule. However, when the temperature increases to 413 K, the (13)C and (45)Sc NMR spectra show that the cluster rotates rapidly inside the C(2v)(5)-C(80) cage, featuring two equivalent Sc atoms and weaker metal-cage interactions.     

Sc2@C3v(8)-C82 vs. Sc2C2@C3v(8)-C82: drastic effect of C2 capture on the redox properties of scandium metallofullerenes

We describe the first example of scandium dimetallofullerenes, Sc(2)@C(3v)(8)-C(82), which has the same cage as the previously assigned scandium carbide cluster fullerene Sc(2)C(2)@C(3v)(8)-C(82) but they exhibit distinctly different electronic configurations and electronic behaviours, confirming the drastic influence of the internal C(2) unit.     

The shape of the Sc2(μ2-S) unit trapped in C82: crystallographic, computational, and electrochemical studies of the isomers, Sc2(μ2-S)@C(s)(6)-C82 and Sc2(μ2-S)@C(3v)(8)-C82

Single-crystal X-ray diffraction studies of Sc(2)(μ(2)-S)@C(s)(6)-C(82)·Ni(II)(OEP)·2C(6)H(6) and Sc(2)(μ(2)-S)@C(3v)(8)-C(82)·Ni(II)(OEP)·2C(6)H(6) reveal that both contain fully ordered fullerene cages. The crystallographic data for Sc(2)(μ(2)-S)@C(s)(6)-C(82)·Ni(II)(OEP)·2C(6)H(6) show two remarkable features: the presence of two slightly different cage sites and a fully ordered molecule Sc(2)(μ(2)-S)@C(s)(6)-C(82) in one of these sites. The Sc-S-Sc angles in Sc(2)(μ(2)-S)@C(s)(6)-C(82) (113.84(3)°) and Sc(2)(μ(2)-S)@C(3v)(8)-C(82) differ (97.34(13)°). This is the first case where the nature and structure of the fullerene cage isomer exerts a demonstrable effect on the geometry of the cluster contained within. Computational studies have shown that, among the nine isomers that follow the isolated pentagon rule for C(82), the cage stability changes markedly between 0 and 250 K, but the C(s)(6)-C(82) cage is preferred at temperatures ≥250 °C when using the energies obtained with the free encapsulated model (FEM). However, the C(3v)(8)-C(82) cage is preferred at temperatures ≥250 °C using the energies obtained by rigid rotor-harmonic oscillator (RRHO) approximation. These results corroborate the fact that both cages are observed and likely to trap the Sc(2)(μ(2)-S) cluster, whereas earlier FEM and RRHO calculations predicted only the C(s)(6)-C(82) cage is likely to trap the Sc(2)(μ(2)-O) cluster. We also compare the recently published electrochemistry of the sulfide-containing Sc(2)(μ(2)-S)@C(s)(6)-C(82) to that of corresponding oxide-containing Sc(2)(μ(2)-O)@C(s)(6)-C(82).     

Understanding the stabilization of metal carbide endohedral fullerenes m(2)c(2)@c(82) and related systems

We analyze the electronic structure of carbide endohedral metallofullerenes of the type Sc(2)C(2)@C(82) and study the possibility of rotation of the encapsulated Sc(2)C(2) moiety in the interior of the cage. Moreover, we rationalize the higher abundance of M(2)C(2)@C(82) (M = Sc, Y) in which the metal-carbide cluster is encapsulated in the C(3v)-C(82):8 carbon cage with respect to other carbides of the same family on the basis of the formal transfer of four electrons from the cluster to the cage and sizeable (LUMO-3)-(LUMO-2) gap in the empty cages. This rule also applies to all those endohedral metallofullerenes in which the encapsulated cluster transfers four electrons to the carbon cage as, for example, the reduced [M@C(82)](-) systems (M = group 3 or lanthanide metal ion).     

Tunable charge-transport properties of I(h)-C80 endohedral metallofullerenes: investigation of La2@C80, Sc3N@C80, and Sc3C2@C80

Fullerene crystals or films have drawn much interest because they are good candidates for use in the construction of electronic devices. The results of theoretical calculations revealed that the conductivity properties of I(h)-C(80) endohedral metallofullerenes (EMFs) vary depending on the encapsulated metal species. We experimentally investigated the solid-state structures and charge-carrier mobilities of I(h)-C(80) EMFs La(2)@C(80), Sc(3)N@C(80), and Sc(3)C(2)@C(80). The thin film of Sc(3)C(2)@C(80) exhibits a high electron mobility μ = 0.13 cm(2) V(-1) s(-1) under normal temperature and atmospheric pressure, as determined using flash-photolysis time-resolved microwave conductivity measurements. This electron mobility is 2 orders of magnitude higher than the mobility of La(2)@C(80) or Sc(3)N@C(80).     

Structural elucidation and regioselective functionalization of an unexplored carbide cluster metallofullerene Sc2C2@C(s)(6)-C82

A Sc(2)C(84) isomer, previously assumed to be Sc(2)@C(84), is unambiguously identified as a new carbide cluster metallofullerene Sc(2)C(2)@C(s)(6)-C(82) using both NMR spectroscopy and X-ray crystallography. The (13)C-nuclei signal of the internal C(2)-unit was observed at 244.4 ppm with a 15% (13)C-enriched sample. Temperature-dependent dynamic motion of the internal Sc(2)C(2) cluster is also revealed with NMR spectrometry. Moreover, the chemical property of Sc(2)C(2)@C(s)(6)-C(82) is investigated for the first time using 3-triphenylmethyl-5-oxazolidinone (1) which provides a 1,3-dipolar reagent under heating. Regarding the low cage symmetry of this endohedral which contains 44 types of nonequivalent cage carbons, it is surprising to find that only one monoadduct isomer is formed in the reaction. Single-crystal X-ray results of the isolated pyrrolidino derivative Sc(2)C(2)@C(s)(6)-C(82)N(CH(2))(2)Trt (2) reveal that the addition takes place at a [6,6]-bond junction, which is far from either of the two Sc atoms. Such a highly regioselective addition pattern can be reasonably interpreted by analyzing the frontier molecular orbitals of the endohedral. Electronic and electrochemical investigations reveal that adduct 2 has a larger highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap than pristine Sc(2)C(2)@C(s)(6)-C(82); accordingly, it is more stable.     

Nanoscale fullerene compression of an yttrium carbide cluster

The nanoscale parameters of metal clusters and lattices have a crucial influence on the macroscopic properties of materials. Herein, we provide a detailed study on the size and shape of isolated yttrium carbide clusters in different fullerene cages. A family of diyttrium endohedral metallofullerenes with the general formula of Y(2)C(2n) (n = 40-59) are reported. The high field (13)C nuclear magnetic resonance (NMR) and density functional theory (DFT) methods are employed to examine this yttrium carbide cluster in certain family members, Y(2)C(2)@D(5)(450)-C(100), Y(2)C(2)@D(3)(85)-C(92), Y(2)C(2)@C(84), Y(2)C(2)@C(3v)(8)-C(82), and Y(2)C(2)@C(s)(6)-C(82). The results of this study suggest that decreasing the size of a fullerene cage with the same (Y(2)C(2))(4+) cluster results in nanoscale fullerene compression (NFC) from a nearly linear stretched geometry to a constrained "butterfly" structure. The (13)C NMR chemical shift and scalar (1)J(YC) coupling parameters provide a very sensitive measure of this NFC effect for the (Y(2)C(2))(4+) cluster. The crystal structural parameters of a previously reported metal carbide, Y(2)C(3) are directly compared to the (Y(2)C(2))(4+) cluster in the current metallofullerene study.     

Electronic structure and redox properties of the open-shell metal-carbide endofullerene Sc3C2@C80: a density functional theory investigation

Density functional theory calculations have shown that the open-shell metal-carbide endofullerene Sc3C2@C80 has the valence state (Sc3+)3(C2)(3-)@C80(6-). A lot of low-lying isomers differing in geometries and locations of the endohedral [(Sc3+)3(C2)(3-)] cluster have been located, indicating unusual dual intramolecular dynamic behaviors of this endofullerene at room temperature. The electrochemical redox properties of this endofullerene have been elucidated in terms of electronic structure theory. Its redox states are found to follow the general charge-state formula (Sc3+)3C2(3-q)-@C80(6-) (q is the charge of the whole molecule ranging from +1 to -3), demonstrating the high charge flexibility of the endohedral metal-carbide cluster. The structure of the endohedral [(Sc3+)3C2(3-q)-)] cluster varies with the redox processes, shifting from a planar structure (for q = 0 and -1) to a trifoliate structure (for q = +1, -2, -3).     

Violating the isolated pentagon rule (IPR): endohedral non-IPR C98 cages of Gd2@C98

The geometric, electronic structure, and thermodynamic stability of large gadolinium-containing endohedral metallofullerenes, Gd(2)@C(98), have been systematically investigated by comprehensive density functional theory calculations combined with statistical mechanics treatments. The Gd(2)@C(2)(230924)-C(98) structure, which satisfies the isolated-pentagon rule (IPR), is determined to possess the lowest energy followed with some stable non-IPR isomers. In order to clarify the relative stabilities at elevated temperatures, entropy contributions are taken into account on the basis of the Gibbs energy at the B3LYP level for the first time. Interestingly, a novel non-IPR Gd(2)@C(1)(168785)-C(98) isomer which has one pair of pentagon adjacency is more thermodynamically stable than the lowest energy IPR species within a wide temperature interval related to fullerene formation. Therefore, the Gd(2)@C(1)(168785)-C(98) is predicted to be the most proper isomer obtained experimentally, which is the largest non-IPR carbon cage found so far. Our findings demonstrate that interaction between metals and carbon cages could stabilize the fused pentagons effectively, and thus, the non-IPR isomers should not be ignored in some cases of endohedral metallofullerenes. The IR features of Gd(2)@C(98) are simulated to assist its future experimental characterization.     

Unprecedented mu4-C2(6-) anion in Sc4C2@C80

Metal carbide compound containing highly charged C2(q-) (q = 5, 6) moiety is rather scarce. We show by means of density functional calculations that an unprecedented mu4-C2(6-) anion can viably exist as an endohedral [Sc4C2]6+ cluster in the endofullerene Sc4C2@C80. The electronic structure, ionization energy, electron affinity, 13C NMR chemical shifts, vibrational frequencies, and electrochemical redox potentials of this unique endofullerene have been predicted to assist future experimental characterization.     

Synthesis, isolation, and addition patterns of trifluoromethylated D5h and I(h) isomers of Sc3N@C80: Sc3N@D5h-C80(CF3)18 and Sc3N@I(h)-C80(CF3)14

Sc(3)N@D(5h)-C(80) and Sc(3)N@I(h)-C(80) were trifluoromethylated with CF(3)I at 400 °C, affording mixtures of CF(3) derivatives. After separation with HPLC, the first multi-CF(3) derivative of Sc(3)N@D(5h)-C(80), Sc(3)N@D(5h)-C(80)(CF(3))(18), and three new isomers of Sc(3)N@I(h)-C(80)(CF(3))(14) were investigated by X-ray crystallography. The Sc(3)N@D(5h)-C(80)(CF(3))(18) molecule is characterized by a large number of double C-C bonds and benzenoid rings within the D(5h)-C(80) cage and a fully different position of the Sc(3)N unit compared to that in the pristine Sc(3)N@D(5h)-C(80). A detailed comparison of five Sc(3)N@I(h)-C(80)(CF(3))(14) isomers reveals a strong influence of the exohedral additions on the behavior of the Sc(3)N cluster inside the I(h)-C(80) cage.     

Sc2S@C(s)(10528)-C72: a dimetallic sulfide endohedral fullerene with a non isolated pentagon rule cage

A non isolated pentagon rule metallic sulfide clusterfullerene, Sc(2)S@C(s)(10528)-C(72), has been isolated from a raw mixture of Sc(2)S@C(2n) (n = 35-50) obtained by arc-discharging graphite rods packed with Sc(2)O(3) and graphite powder under an atmosphere of SO(2) and helium. Multistage HPLC methods were utilized to isolate and purify the Sc(2)S@C(72). The purified Sc(2)S@C(s)(10528)-C(72) was characterized by mass spectrometry, UV-vis-NIR absorption spectroscopy, cyclic voltammetry, and single-crystal X-ray diffraction. The crystallographic analysis unambiguously elucidated that the C(72) fullerene cage violates the isolated pentagon rule, and the cage symmetry was assigned to C(s)(10528)-C(72). The electrochemical behavior of Sc(2)S@C(s)(10528)-C(72) shows a major difference from those of Sc(2)S@C(s)(6)-C(82) and Sc(2)S@C(3v)(8)-C(82) as well as the other metallic clusterfullerenes. Computational studies show that the Sc(2)S cluster transfers four electrons to the C(72) cage and C(s)(10528)-C(72) is the most stable cage isomer for both empty C(72)(4-) and Sc(2)S@C(72), among the many possibilities. The structural differences between the reported fullerenes with C(72) cages are discussed, and it is concluded that both the transfer of four electrons to the cage and the geometrical requirements of the encaged Sc(2)S cluster play important roles in the stabilization of the C(s)(10528)-C(72) cage.     

Crystallographic X-ray analyses of Yb@C(2v)(3)-C80 reveal a feasible rule that governs the location of a rare earth metal inside a medium-sized fullerene

Single crystal X-ray diffraction studies of Yb@C(2v)(3)-C(80)·Ni(II)(OEP)·CS(2)·1.5C(6)H(6) (OEP = octaethylporphinate) reveal that a relatively flat region of the fullerene interacts with the Ni(II)(OEP) molecule, featuring shape-matching interactions. Surprisingly, it is found that the internal metal is located under a hexagonal carbon ring apart from the 2-fold axis of the C(2v)(3)-C(80) cage, presenting the first example of metallofullerenes with an asymmetrically positioned metal. Such an anomalous location of Yb(2+) is associated with its strong ability to pursue a large coordination number and the lack of hexagon along the C(2) axis of C(2v)(3)-C(80). It is accordingly assumed that a suitable cage hexagon is most likely to be preferred by the single rare earth metal to stay behind inside a medium-sized fullerene, such as C(80) and C(82).     

Bonding between strongly repulsive metal atoms: an oxymoron made real in a confined space of endohedral metallofullerenes

Endohedral metallofullerenes (EMFs) are able to encapsulate up to four metal atoms. In EMFs, metal atoms are positively charged because of the electron transfer from the endohedral metal atoms to the carbon cage. It results in the strong Coulomb repulsion between the positively charged ions trapped in the confined inner space of the fullerene. At the same time, in many EMFs, such as Lu(2)@C(76), Y(2)@C(79)N, M(2)@C(82) (M = Sc, Y, Lu, etc.), Y(3)@C(80), or Sc(4)O(2)@C(80), metals do not adopt their highest oxidation states, thus yielding a possibility of the covalent metal-metal bonding. In some other EMFs (e.g., La(2)@C(80)), metal-metal bonding evolves as the result of the electrochemical or chemical reduction, which leads to the population of the metal-based LUMO with pronounced metal-metal bonding character. This article highlights different aspects of the metal-metal bonding in EMFs. It is concluded that the valence state of the metal atoms in dimetallofullerenes is not dependent on their third ionization potential, but is determined by their ns(2)(n- 1)d(1)→ns(1)(n- 1)d(2) excitation energies. Peculiarities of the metal-metal bonding in EMFs are described in terms of molecular orbital analysis as well as topological approaches such as Quantum Theory of Atoms in Molecules and Electron Localization Function. Interplay of Coulomb repulsion and covalent bonding is analyzed in the framework of the Interacting Quantum Atom approach.     

Large endohedral fullerenes containing two metal ions, Sm2@D2(35)-C88, Sm2@C1(21)-C90, and Sm2@D3(85)-C92, and their relationship to endohedral fullerenes containing two gadolinium ions

The carbon soot obtained by electric arc vaporization of carbon rods doped with Sm(2)O(3) contains a series of monometallic endohedral fullerenes, Sm@C(2n), along with smaller quantities of the dimetallic endohedrals Sm(2)@C(2n) with n = 44, 45, 46, and the previously described Sm(2)@D(3d)(822)-C(104). The compounds Sm(2)@C(2n) with n = 44, 45, 46 were purified by high pressure liquid chromatography on several different columns. For endohedral fullerenes that contain two metal atoms, there are two structural possibilities: a normal dimetallofullerene, M(2)@C(2n), or a metal carbide, M(2)(μ-C(2))@C(2n-2). For structural analysis, the individual Sm(2)@C(2n) endohedral fullerenes were cocrystallized with Ni(octaethylporphyrin), and the products were examined by single-crystal X-ray diffraction. These data identified the three new endohedrals as normal dimetallofullerenes and not as carbides: Sm(2)@D(2)(35)-C(88), Sm(2)@C(1)(21)-C(90), and Sm(2)@D(3)(85)-C(92). All four of the known Sm(2)@C(2n) endohedral fullerenes have cages that obey the isolated pentagon rule (IPR). As the cage size expands in this series, so do the distances between the variously disordered samarium atoms. Since the UV/vis/NIR spectra of Sm(2)@D(2)(35)-C(88) and Sm(2)@C(1)(21)-C(90) are very similar to those of Gd(2)C(90) and Gd(2)C(92), we conclude that Gd(2)C(90) and Gd(2)C(92) are the carbides Gd(2)(μ-C(2))@D(2)(35)-C(88) and Gd(2)(μ-C(2))@C(1)(21)-C(90), respectively.     

Synthesis and charge-transfer chemistry of La2@I(h)-C80/Sc3N@I(h)-C80-zinc porphyrin conjugates: impact of endohedral cluster

Two stable electron donor-acceptor conjugates, that is, 3 and 5b, employing La(2)@I(h)-C(80) and Sc(3)N@I(h)-C(80), on one hand, and zinc tetraphenylporphyrin, on the other hand, have been prepared via [1+2] cycloaddition reactions of a diazo precursor. Combined studies of crystallography and NMR suggest a common (6,6)-open addition pattern of 3 and 5b. Still, subtly different conformations, that is, a restricted and a comparatively more flexible topography, emerge for 3 and 5b, respectively. In line with this aforementioned difference are the electrochemical assays, which imply appreciably stronger I(h)-C(80)/ZnP interactions in 3 when compared to those in 5b. Density functional calculations reveal significant attractions between the two entities of these conjugates, as well as their separately localized HOMOs and LUMOs. The geometrical conformations and LUMO distributions of 3 and 5b, at our applied computational level, are slightly varied with their different endohedral clusters. The clusters also exert different impact on the excited state reactivity of the conjugates. For example, 3 undergoes, upon photoexcitation, a fast charge separation process and yields a radical ion pair, whose nature, namely, (La(2)@C(80))(?-)-(ZnP)(?+)) versus (La(2)@C(80))(?+)-(ZnP)(?-)), varies with solvent polarity. 5b, on the other hand, afforded the same (Sc(3)N@C(80))(?-)-(ZnP)(?+)) radical ion pair regardless of the solvent.     

Sc2@C70 rather than Sc2C2@C68: density functional theory characterization of metallofullerene Sc2C70

Detailed study on Sc(2)C(70) series has been performed based on fully screening for C(70) tetra- and hexa- anions. With a combined methodology of quantum chemistry and statistical mechanics, our calculation results reveal that the Sc(2)C(70), which was proposed as the first metal-carbide endohedral metallofullerene with a non-isolated pentagon rule (non-IPR) cage (Sc(2)C(2)@C(68):6073_C(2v)), is in fact a C(70) non-IPR metallofullerene structure (Sc(2)@C(70):7854_C(2v)) with three pair of pentagon adjacency thanks to its significant thermodynamic and kinetic stability. According to the natural bond analysis and orbital interaction diagram, each scandium atom should only transfer two 4s electrons to the carbon cages and the valence state of Sc(2)@C(70) is (Sc(2+))(2)@C(70) (4-). In addition, the simulation of UV-Vis-NIR spectrum for Sc(2)@C(70):7854_C(2v) shows good accordance to the experimental spectrum.     

La2@C72 and Sc2@C72: computational characterizations

The La2@C72 and Sc2@C72 metallofullerenes have been characterized by systematic density functional computations. On the basis of the most stable geometry of 39 C72 hexaanions and the computed energies of the best endofullerene candidates, the experimentally isolated La2@C72 species was assigned the structure coded #10611. The good agreement between the computed and the experimental 13C chemical shifts for La2@C72 further supports the literature assignment (Kato, H.; Taninaka, A.; Sugai, T.; Shinohara, H. J. Am. Chem. Soc. 2003, 125, 7782). The geometry, IR vibrational frequencies, and 13C chemical shifts of Sc2@C72 were predicted to assist its future experimental characterization.     

Structure, stability, and cluster-cage interactions in nitride clusterfullerenes M3N@C2n (M = Sc, Y; 2n = 68-98): a density functional theory study

Extensive semiempirical calculations of the hexaanions of IPR (isolated pentagon rule) and non-IPR isomers of C(68)-C(88) and IPR isomers of C(90)-C(98) followed by DFT calculations of the lowest energy structures were performed to find the carbon cages that can provide the most stable isomers of M(3)N@C(2n) clusterfullerenes (M = Sc, Y) with Y as a model for rare earth ions. DFT calculations of isomers of M(3)N@C(2n) (M = Sc, Y; 2n = 68-98) based on the most stable C(2n)(6-) cages were also performed. The lowest energy isomers found by this methodology for Sc(3)N@C(68), Sc(3)N@C(78), Sc(3)N@C(80), Y(3)N@C(78), Y(3)N@C(80), Y(3)N@C(84), Y(3)N@C(86), and Y(3)N@C(88) are those that have been shown to exist by single-crystal X-ray studies as Sc(3)N@C(2n) (2n = 68, 78, 80), Dy(3)N@C(80), and Tb(3)N@C(2n) (2n = 80, 84, 86, 88) clusterfullerenes. Reassignment of the carbon cage of Sc(2)@C(76) to the non-IPR Cs: 17490 isomer is also proposed. The stability of nitride clusterfullerenes was found to correlate well with the stability of the empty 6-fold charged cages. However, the dimensions of the cage in terms of its ability to encapsulate M(3)N clusters were also found to be an important factor, especially for the medium size cages and the large Y(3)N cluster. In some cases the most stable structures are based on the different cage isomers for Sc(3)N and Y(3)N clusters. Up to the cage size of C(84), non-IPR isomers of C(2n)(6-) and M(3)N@C(2n) were found to compete with or to be even more stable than IPR isomers. However, the number of adjacent pentagon pairs in the most stable non-IPR isomers decreases as cage size increases: the most stable M(3)N@C(2n) isomers have three such pairs for 2n = 68-72, two pairs for n = 74-80, and only one pair for n = 82, 84. For C(86) and C(88) the lowest energy IPR isomers are much more stable than any non-IPR isomer. The trends in the stability of the fullerene isomers and the cluster-cage binding energies are discussed, and general rules for stability of clusterfullerenes are established. Finally, the high yield of M(3)N@C(80) (Ih) clusterfullerenes for any metal is explained by the exceptional stability of the C(80)(6-) (Ih: 31924) cage, rationalized by the optimum distribution of the pentagons leading to the minimization of the steric strain, and structural similarities of C(80) (Ih: 31924) with the lowest energy non-IPR isomers of C(760(6-), C(78)(6-), C(82)(6-), and C(84)(6-) pointed out.