High-Resolution X-ray Photoelectron Spectroscopy of Organometallic (CHSiMe)Ln and [(CHSiMe)Ln] Complexes (Ln = Sm, Eu, Gd, Tb).

The capacity of X-ray photoelectron spectroscopy (XPS) to provide information on the electronic structure of molecular organometallic complexes of Ln(II) ions (Ln = lanthanide) has been examined for the first time. XPS spectra were obtained on the air-sensitive molecular trivalent 4f Cp'Ln complexes (Ln = Sm, Eu, Gd, Tb; Cp' = CHSiMe) and compared to those of the highly reactive divalent complexes, [K(crypt)][Cp'Ln] (crypt = 2.2.2-cryptand), which have either 4f (Sm, Eu) or 4f5d electron configurations (Gd, Tb). The Ln 4d, Si 2p, and C 1s regions of the Ln(III) and Ln(II) complexes were identified and compared. The metal 4d peaks of these molecular lanthanide complexes were used diagnostically to compare oxidation states. The valence region of the Gd(III) and Gd(II) complexes was also examined with XPS and density function theory/random phase approximation (DFT/RPA) calculations, and this led to the tentative assignment of a signal from the 5d electron consistent with a 4f5d electron configuration for Gd(II).