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

Abstract

A series of computational experiments performed with various methods belonging to wave-function and density functional theories approaches the issue of bonding regime and exchange coupling in the title compounds. Gd 2 @C 80 is computed with a very weak exchange coupling, the sign depending on the method, while Gd 2 @C 79 N has resulted with a strong coupling and ferromagnetic ground state, irrespective of the computational approach. The multi-configuration calculation and broken symmetry estimation are yielding closely coincident coupling constants, of about J ∼ 400 cm −1 . No experimental estimation exists, but the ferromagnetic ground state of Gd 2 @C 79 N is confirmed from paramagnetic resonance data. The different behaviour is due to particularities of electron accommodation in the orbital scheme. The exchange effects localised on atom lead to preference for parallel alignment of the electrons placed in the 4f and 5d lanthanide shells, determining also a ferromagnetic inter-centre coupling. The structural insight is completed with a ligand field analysis of the density functional theory results in the context of frozen density embedding. The energy decomposition analysis of bonding effects is also discussed. Finally, with the help of home-made codes (named Xatom+Xsphere), a model for the atom encapsulated in a cage is designed, the exemplified numeric experiments showing relevance for the considered endohedral metallo-fullerene issues.

Single molecule magnet with an unpaired electron trapped between two lanthanide ions inside a fullerene

“…31 and Supplementary Note 10). Similar large values were predicted recently for Gd 2 @C 79 N (refs 35, 36) and the EPR study of the latter revealed a S =15/2 ground state, which points to the ferromagnetic coupling of all spins in the [Gd 3+ – e –Gd 3+ ] system34. These parameters can be compared with the [Gd 3+ –N 2 3− –Gd 3+ ] complex with a radical bridge, in which Gd ions are antiferromagnetically coupled to the electron spin of the N 2 3− bridge with the j Gd, e value of −27 cm −1 (ref.…”

“…A single-electron M–M bond has been also stabilized by a substitution of one carbon atom by nitrogen, giving azafullerenes M 2 @C 79 N (M=Y, Gd, Tb)3334. Computational studies predicted a large ferromagnetic coupling of Gd ions in Gd 2 @C 79 N (refs 35, 36) and unusual magnetic properties in Dy 2 @C 79 N (ref. 35).…”

Development and applications of the LFDFT: the non-empirical account of ligand field and the simulation of the f–d transitions by density functional theory

“…They were computed in the LFDFT algorithm using the following non-empirical parameters: F k (ff) and z 4f ( Table 2); F k (fd), G k (fd), z 5d and D(fd) ( Table 6); and B k q 's parameters ( Table 5). The transitions from the initial 4f 7 ( 8 S 7/2 ) state to the final 4f 6 5d 1 are electric dipole-allowed, with the calculation of the electric dipole transition moments obtained from eqn (15). The oscillator strength for the zero phonon lines between the ground state 8 S 7/2 of 4f 7 and the final states of 4f 6 5d 1 are calculated and represented in Fig.…”

Electronic Structure and Photoluminescence Properties of Eu(η9-C9H9)2

“…We note also that the ligand−field splitting of the Eu 5d orbitals is 30 times larger than that obtained for Eu 4f, the Eu 5d being more available for bonding properties. 15,57 The calculated parentage coefficients of Eu(η 9 -C 9 H 9 ) 2 from Eu 5d are relatively weak (see Table 5). Namely, we obtained circa 43% for 5d σ .…”