Gd₂@C₇₉N: Isolation, Characterization, and Monoadduct Formation of a Very Stable Heterofullerene with a Magnetic Spin State of S = 15/2

Abstract

The dimetallic endohedral heterofullerene (EHF), Gd2@C79N, was prepared and isolated in a relatively high yield when compared with the earlier reported heterofullerene, Y2@C79N. Computational (DFT), chemical reactivity, Raman, and electrochemical studies all suggest that the purified Gd2@C79N, with the heterofullerene cage, (C79N)5- has comparable stability with other better known isoelectronic metallofullerene (C80)6- cage species (e.g., Gd3N@C80). These results describe an exceptionally stable paramagnetic molecule with low chemical reactivity with the unpaired electron spin density localized on the internal diatomic gadolinium cluster and not on the heterofullerene cage. EPR studies confirm that the spin state of Gd2@C79N is characterized by a half-integer spin quantum number of S = 15/2. The spin (S = 1/2) on the N atom of the fullerene cage and two octet spins (S = 7/2) of two encapsulated gadoliniums are coupled with each other in a ferromagnetic manner with a small zero-field splitting parameter D. Because the central line of Gd2@C79N is due to the Kramer's doublet with a half-integer spin quantum number of S = 15/2, this relatively sharp line is prominent and the anisotropic nature of the line is weak. Interestingly, in contrast with most Gd3+ ion environments, the central EPR line (g=1.978) is observable even at room temperature in a toluene solution. Finally, we report the first EHF derivative, a diethyl bromomalonate monoadduct of Gd2@C79N, was prepared and isolated via a modified Bingel-Hirsch reaction.

On exchange coupling and bonding in the Gd2@C80 and Gd2@C79N endohedral dimetallo-fullerenes

“…The reported ferromagnetism of the Gd 2 @C 79 N and other structural features were previously sustained [18] with thorough experimental investigations, based on electron paramagnetic resonance. This work [18] also included state of the art DFT calculations but do not advanced toward the computation of the exchange coupling, as the experimental data do not afforded its estimation.…”

“…The presented sequence clearly illustrates the pattern of the exchange, based on a large J MX ferromagnetic coupling, the fitted values being J MX = 407.11 cm −1 and J MM = 0.011 cm −1 . Unfortunately, the experimental data do not allow the fit of the coupling parameters, the ferromagnetic nature of the ground state being known only from electron paramagnetic resonance [18].…”

“…Though not bonded, the ions of the lanthanide couple should show magnetic interactions whose nature is interesting, in circumstances of enforced mutual encounter. An interesting case, on which we will focus in the following, is the Gd 2 @C 79 N molecule, reported as a ferromagnetic coupling between the two gadolinium ions [18]. The Gd 2 @C 79 N di-metallo-heterofullerene is formally derived from Gd 2 @C 80 with icosahedral symmetry of the cage, a comparison between the two systems being considered.…”

“…This work [18] also included state of the art DFT calculations but do not advanced toward the computation of the exchange coupling, as the experimental data do not afforded its estimation. We give in the following the complementary account.…”

Enhanced magnetism of Cun clusters capped with N and endohedrally doped with Cr

“…For example, while there is no appreciable spin density on an empty cage of C 80 fullerene, the cluster-fullerene Gd 3 N@C 80 forms a stable magnetic unit with high magnetic moment which is largely contributed by the localized f electrons of the Gd atoms. [18] Enhanced magnetic moments of a cagelike icosahedral M 13 clusters ( M = metal atom ) upon appropriate substitution at the central site, has been examined extensively. [19] Since the N capped Cu n clusters are interesting for magnetic applications, it is essential to explore the possibilities of engineering its magnetic properties further.…”