High-spin electronic states of lanthanide-arene complexes: Nd(benzene) and Nd(naphthalene)

Neodymium (Nd) complexes of benzene and naphthalene were synthesized in a laser-ablation supersonic molecular beam source. High-resolution electron spectra of these complexes were obtained using pulsed-field ionization zero electron kinetic energy (ZEKE) spectroscopy. Second-order Møller-Plesset perturbation calculations were employed to aid spectral and electronic-state assignments. The adiabatic ionization energies were measured to be 38 081 (5) cm −1 for Nd(benzene) and 37 815 (5) cm −1 for Nd(naphthalene). For the Nd(benzene) complex, the observed frequencies of 831 and 286 cm −1 were assigned to C-H out-of-plane bending and Nd + -C 6 H 6 stretching modes in the 6 A 1 ion state and 256 cm −1 to the Nd-C 6 H 6 stretching mode in the 7 A 1 neutral state. To confirm these assignments, the ZEKE spectrum of the deuterated species was recorded, and the corresponding vibrational frequencies were measured to be 710 and 277 cm −1 in the ion state and 236 cm −1 in the neutral state. For the Nd(naphthalene) complex, the observed vibrational modes were C 10 H 8 bending (394 cm −1 ), Nd + -C 10 H 8 stretching (286 and 271 cm −1 ), Nd + -C 10 H 8 bending (80 cm −1 ), and C 10 H 8 twisting (105 cm −1 ) in the 6 A ′ ion state and metal-ligand bending (60 cm −1 ) and ligand twisting (55 cm −1 ) in the 7 A ′ neutral state. The formation of the ground state of the Nd(benzene) complex requires 4 f → 5 d and 6 s → 5 d electron excitation of the Nd atom, whereas the formation of the ground state of Nd(naphthalene) involves the 6 s → 5 d electron promotion.