Two isomers of Sm@C-92 and four isomers of Sm@C-94 were isolated from carbon soot obtained by electric arc vaporization of carbon rods doped with Sm2O3. Analysis of the structures by single-crystal X-ray diffraction on cocrystals formed with Ni-II(octaethylporphyrin) reveals the identities of two of the Sm@C-92 isomers: Sm@C-92(I), which is the more abundant isomer, is Sm@C-1(42)-C-92, and Sm@C-92(II) is Sm@C-s(24)-C-92. The structure of the most abundant form of the four isomers of Sm@C-94, Sm@C-94(1), is Sm@C-3v(134)-C-94, which utilizes the same cage isomer as the previously known Ca@C-3v(134)-C-94 and Tm@C-3v(134)-C-94. All of the structurally characterized isomers obey the isolated pentagon rule. While the four Sm@C-90 and five isomers of Sm@C-84 belong to common isomerization maps that allow these isomers to be interconverted through Stone-Wales transformations, Sm@C-1(42)-C-92 and Sm@C-s(24)-C-92 are not related to each other by any set of Stone-Wales transformations. UV-vis-NIR spectroscopy and computational studies indicate that Sm@C-1(42)-C-92 is more stable than Sm@C-s(24)-C-92 but possesses a smaller HOMO-LUMO gap. While the electronic structures of these endohedrals can be formally described as Sm2+@C-2n(2-), the net charge transferred to the cage is less than two due to some back-donation of electrons from pi orbitals of the cage to the metal ion.