Stability calculations for Eu@C₇₄ isomers

Density functional theory (DFT) calculations are reported for Eu@C ₇₄, where the considered C₇₄ cage is either the IPR (isolated pentagon rule) species or two cages with a pentagon-pentagon junction. Their relative thermodynamic production yields are evaluated using the DFT calculated terms and it is shown that the IPR-based Eu@C₇₄ endohedral prevails at relevant temperatures in agreement with observation, however, isolation of a minor isomer should be possible. The question of whether C ₇₄-based metallofullerenes present isomeric forms is still an object of debate. In the case of Eu@C₇₄ density functional theory calculations predict that in addition to the dominant endohedral species (in which none of the pentagons in the C₇₄ cage make contact with each, in respect to the isolated pentagon rule, IPR), a non-IPR isomer should exist and could possibly even be isolated.