MonometallofullereneTm@C82: Proof of an Encapsulated Divalent Tm Ion by High-Energy Spectroscopy

The valency of the Tm ion in the endohedral monometallofullerene ${\mathrm{T}\mathrm{m}@\mathrm{C}}_{82}$ with $C_{3v}$ symmetry has been studied using high-energy spectroscopy. The resemblance of the Tm $4d$ core level photoemission spectrum to that calculated for ${\mathrm{Yb}}^{3+}$ suggests a ${4f}^{13}$ ground state configuration for the encapsulated Tm ion. This could be proven beyond doubt by measurements of the characteristic $4f$ multiplet structure in photoemission. Furthermore, the Tm $4d$ excitation spectrum measured using volume sensitive electron energy-loss measurements in transmission confirms that this material is indeed the first monometallofullerene containing a divalent lanthanide ion.