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 Moller-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 286cm ^-1 were assigned to C-H out-of-plane bending and Nd ⁺-C ₆H ₆ stretching modes in the ⁶A ₁ ion state and 256cm ^-1 to the Nd-C ₆H ₆ stretching mode in the ⁷A 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 277cm ^-1 in the ion state and 236cm ^-1 in the neutral state. For the Nd(naphthalene) complex, the observed vibrational modes were C ₁₀H ₈ bending (394cm ^-1), Nd ⁺-C ₁₀H ₈ stretching (286 and 271cm ^-1), Nd ⁺-C ₁₀H ₈ bending (80cm ^-1), and C ₁₀H ₈ twisting (105cm ^-1) in the ⁶A ^′ ion state and metal-ligand bending (60cm ^-1) and ligand twisting (55cm ^-1) in the ⁷A ^′ neutral state. The formation of the ground state of the Nd(benzene) complex requires 4f → 5d and 6s → 5d electron excitation of the Nd atom, whereas the formation of the ground state of Nd(naphthalene) involves the 6s → 5d electron promotion.