Multifrequency EPR Study of Metallofullerenes:  Eu@C₈₂ and Eu@C₇₄

Abstract

In this work, the cage structure of a family of europium metallofullerenes, Eu@C 74 and three isomers of Eu@C 82 , were investigated. The analogy of the electronic states of three isomers of Eu@C 82 with those of three isomers of Ca@C 82 was confirmed by UV-vis-near-IR absorption spectra. The symmetries C s , C 2 , and C 2V were assigned for three isomers of Eu@C 82 by comparing each corresponding isomer of Ca@C 82 . The D 3h cage structure of Eu@C 74 , which is expected only for the C 74 from the isolated pentagon rule, was also confirmed by comparing its photoabsorption spectrum with that of Ca@C 74 . Multifrequency electron paramagnetic resonance (EPR) spectroscopy was employed to determine the zero-field splitting (ZFS) parameters of the metallofullerenes, which are closely related to the surrounding cage structures. The experimental X-and W-band EPR spectra were completely reproduced by computer simulations based on a spin Hamiltonian considering the ZFS terms up to fourth order. The introduction of the fourth-order ZFS terms into the Hamiltonian resulted in a precise determination of the second-order ZFS terms. A nonvanishing rhombicity parameter E of Eu@C 74 demonstrated the reduction of the symmetry from D 3h to C 2V due to the positioning of Eu 2+ ion at the off-center of C 74 cage. Moreover, in this work, the semiphenomenological superposition-exchange model (SPEM) was invoked to examine a relationship between the molecular structures and ZFS parameters. All of the experimental ZFS parameters were satisfactory reproduced in terms of the SPEM, leading to confirmation of the molecular symmetries. The semiphenomenological analysis also enabled us to select the most appropriate cage for Eu@C 82 with C 2 symmetry from among three possible isomers.

Magnetic Properties and Crystal Structure of Solvent‐Free Sc@C82 Metallofullerene Microcrystals

“…[23,35] Recently, ESR measurements of some lanthanide metallofullerenes have been reported. [39][40][41][42] Temperature dependence of the physical properties of such metallofullerene solids or single crystals has been also characterized by ESR, SQUID magnetic measurements [43][44][45][46][47][48][49][50] and X-ray diffraction measurements. [51,52] Antiferromagnetic-like interactions have been observed for powder crystals of La@C 82 , [44] Gd@C 82 [43,44] and heavy rare-earth monometallofullerenes [48] by the SQUID magnetic measurements.…”

Molecular geometries, electronic properties, and vibrational spectroscopic studies of endohedral metallofullerenes TM@C24 and TM@C24H12 (TM = Cr, Mo, and W)

“…Moreover, these properties have also made them prominent species in nanotechnology [2][3][4] and bio-medicine [5][6][7]. Now there have been some previous theoretical and experimental studies on endohedral complexes doped with one metal atom [8][9][10][11][12][13][14][15][16][17][18][19][20]. For example, the stabilizations of C 28 fullerene with four tetrahedral valences have been investigated by mean of laser vaporization experiments and ab initio quantum chemical calculations [8].…”

Computations on three isomers of La@C74

“…W hile empty C 74 fullerene [1] has still not been available, various related C 74 -based metallo-fullerenes have been known and studied vigorously like Ca@C 74 [2,3], Sm@C 74 [4,5], Sr@C 74 [6], Ba@C 74 [7], La@C 74 [8][9][10], Eu@C 74 [11], Yb@C 74 [12][13][14], Sc 2 @C 74 [15], or Er 3 @C 74 [16]. Among them, La@C 74 has a special position as its X-ray crystallographic analysis is available [10], although for a solventrelated derivative, La@C 74 -C 6 H 3 Cl 2 .…”