Magnetic structure of the europium fulleride ferromagnet Eu(6)C(60)

Silvery fullerene in Ag102 nanosaucer

Despite the discovery of a series of fullerenes and a handful of noncarbon clusters with the typical topology of I h-C60, the smallest fullerene with a large degree of curvature, C20, and its other-element counterparts are difficult to isolate experimentally. In coinage metal nanoclusters (NCs), the first all-gold fullerene, Au32, was discovered after a long-lasting pursuit, but the isolation of similar silvery fullerene structures is still challenging. Herein, we report a flying saucer-shaped 102-nuclei silver NC (Ag102) with a silvery fullerene kernel of Ag32, which is embraced by a robust cyclic anionic passivation layer of (KPO4)10. This Ag32 kernel can be viewed as a non-centered icosahedron Ag12 encaged into a dodecahedron Ag20, forming the silvery fullerene of Ag12@Ag20. The anionic layer (KPO4)10 is located at the interlayer between the Ag32 kernel and Ag70 shell, passivating the Ag32 silvery fullerene and templating the Ag70 shell. The t BuPhS- and CF3COO- ligands on the silver shell show a regioselective arrangement with the 60 t BuPhS- ligands as expanders covering the upper and lower of the flying saucer and 10 CF3COO- as terminators neatly encircling the edges of the structure. In addition, Ag102 shows excellent photothermal conversion efficiency (η) from the visible to near-infrared region (η = 67.1% ± 0.9% at 450 nm, 60.9% ± 0.9% at 660 nm and 50.2% ± 0.5% at 808 nm), rendering it a promising material for photothermal converters and potential application in remote laser ignition. This work not only captures silver kernels with the topology of the smallest fullerene C20, but also provides a pathway for incorporating alkali metal (M) into coinage metal NCs via M-oxoanions.

Raman spectroscopic study of the rare-earth fullerides Eu6-xSrxC60

We present Raman spectroscopic studies of the isostructural and isoelectronic Eu(6-x)Sr(x)C(60) (x = 0, 3, 5, 6) and Ba(6)C(60) compounds. The Raman spectra of the Eu-based fullerides show dramatic changes compared to the pure alkaline-earth systems, including significant broadening, splitting and frequency shifts of the fivefold degenerate H(g) intramolecular modes of C(60). Moreover, the A(g)(2) mode exhibits an even larger downshift and a remarkable broadening. These findings are consistent with distortions of the C(60) molecular cages and a considerable electron-phonon coupling strength-strongly enhanced in the Eu containing systems-originating from the strong orbital hybridization between the metal atom and the C(60) molecule.

Electronic structure of Eu-C(70) fullerides

The electronic structure of Eu-intercalated C(70) has been studied by a synchrotron radiation photoemission spectroscopy technique. At low intercalation levels (below the stoichiometry of Eu(3)C(70)), the photoemission data clearly exhibit charge transfer from Eu 6s states to the lowest-unoccupied-molecular-orbital (LUMO) and the LUMO + 1 of C(70). The amount of charge transfer reaches its maximum far before intercalation saturation. Detailed analysis reveals that most of the 5d6s electrons of Eu occupy the so-called interstitial states in the saturation phase (Eu(9)C(70)). The interstitial states are induced by a Eu sub-lattice formed at heavy intercalation levels, and comprise substantial 6s-π hybridized states. The π states participating in the hybridization are mainly the HOMO - n (n = 6-10) orbitals. The PES data also reveal the semiconducting property for both Eu(3)C(70) and Eu(9)C(70). The 6s-(HOMO - n) hybridization and the semiconducting property should play important roles in understanding the ferromagnetic mechanism for Eu(9)C(70).

Mixed valency in rare-earth fullerides

Mixed-valence phenomena associated with the highly correlated narrow-band behaviour of the 4f electrons in rare earths are well documented for a variety of rare-earth chalcogenides, borides and intermetallics (Kondo insulators and heavy fermions). The family of rare-earth fullerides with stoichiometry RE2.75C60 (RE=Sm, Yb, Eu) also displays an analogous phenomenology and a remarkable sensitivity of the rare-earth valency to external stimuli (temperature and pressure) making them the first known molecular-based members of this fascinating class of materials. Using powerful crystallographic and spectroscopic techniques which provide direct indications of what is happening in these materials at the microscopic level, we find a rich variety of temperature- and pressure-driven abrupt or continuous valence transitions-the electronically active fulleride sublattice acts as an electron reservoir that can accept electrons from or donate electrons to the rare-earth 4f/5d bands, thereby sensitively modulating the valence of the rare-earth sublattice.

Synthesis, structure, and magnetic properties of the fullerene-based ferromagnets Eu3C70 and Eu9C70

Intercalation of C(70) with europium affords two kinds of magnetic compounds, a canted antiferromagnet Eu(x)C(70) (x approximately 3) and a ferromagnet Eu(x)C(70) (x approximately 9) with transition temperatures (T(C)) of 5 and 38 K, respectively. The Curie constants in the paramagnetic phase and the saturation moment in the ferromagnetic phase are both understood by the full moment of Eu(2+) for both systems. The structure of Eu(3)(-)(delta)C(70) (delta approximately 0.27) is pseudo-monoclinic, derived by a simple deformation of the parent face-centered cubic (fcc) structure. Eu(9)(-)(delta)C(70) (delta approximately 0.2) forms an fcc structure, in which cuboctahedral clustering of Eu(2+) ions is observed in the enhanced size octahedral holes. The observed T(C) of the Eu(9)(-)(delta)C(70) ferromagnet is comparable to or larger than those of simple binary Eu-based ferromagnets, such as Eu chalcogenides or carbides, despite the low atomic ratio of Eu in the chemical formulas. This can be understood by the short Eu(2+)-Eu(2+) distances and high coordination numbers permitted by the multiple occupation by Eu(2+) ions of the expanded octahedral interstitial sites in higher fullerene-based solids.