Isolation and Characterization of a New Isomer of Ca@C72

We isolated a new (second) isomer of Ca@C 7 2 . As a result of this discovery, it was confirmed that at least one of the two Ca@C 7 2 isomers has a C 7 2 cage that does not satisfy the so-called isolated pentagon rule (IPR), because C 7 2 has only one IPR cage structure.