Comparative EPR study of Cu@C60 and N@C60 endofullerenes

Abstract

A comparative study of C60-based endohedral fullerenes was performed. From an analysis of spin relaxation times of the recently characterized Cu@C60 metallo-endofullerene, it could be shown that the encased ion occupies a well-defined off-centre position even at room temperature. Localization on the timescale of an EPR experiment is combined with charge transfer of approximately two electrons, resulting in the EPR signature of a 3d9 copper ion. This is in contrast to N@C60, for which a nearly complete decoupling from the cage is found. An upper limit for the variance of collision-induced modulation of the anisotropic nitrogen hfi is determined as (A(eff)2)(1/2) < 500 kHz by an analysis of cross peak intensities in a 2D EPR experiment. Pulsed 95 GHZ ENDOR experiments have been performed to confirm that deformation-induced hyperfine anisotropies are expected to be very small in N@C60.

Density functional investigations of endohedral metallofullerenes TM@C24 (TM = Mn, Fe, Co, Ni, Cu, and Zn)

“…So the most stable Cu@C 24 is the 1b isomer in C s symmetry with 2 AЈ state. In the most stable Cu@C 24 , the distance between Cu atom and center is about 0.28 Å, which is agreement with the ESR measurements obtained by Knapp et al, [52] who shown that the encased copper atom occupies a well-defined off-center position even at room temperature.…”

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

“…The Cr atom is deviated from the center of C 24 cage by about 0.311 Å , which is similar to those of TM@C 24 (TM = Mn, Fe, Co, Ni, and Cu) [11] and Ti@C 24 [13]. Further, it is also agreement with the ESR experiments prepared by Knapp et al [61], who reported that the encased copper ion occupies a well-defined offcenter position even at room temperature.…”

On the feasibility of reactions through the fullerene wall: a theoretical study of NHx@C60

“…Thus, the first reaction step (step 1 in Scheme 1) begins from N@C 60 1, which can exist in high-(spin 3/2) and low-spin (spin 1/2) states. It has been shown in previous experimental 2, [70][71][72] and theoretical 4,73,74 studies that the ground state of 1 is high spin. Our current study supports this conclusion, since 4 1 is more stable than 2 1 (see Scheme 2) by 26.0 kcal mol À1 Scheme 1 Proposed approach for step-by-step synthesis of NH 4 + @C 60 À (13).…”