M←NCCH3, M-η2-(NC)-CH3, and CN-M-CH3 Prepared by Reactions of Ce, Sm, Eu, and Lu Atoms with Acetonitrile: Matrix Infrared Spectra and Theoretical Calculations.

The reactions of laser-ablated Ce, Sm, Eu, and Lu atoms with acetonitrile were studied by matrix infrared spectra in a neon matrix, and M←NCCH3, M-η2-(NC)-CH3, and CN-M-CH3 were identified with isotopic substitution and quantum chemical calculations. The major product is the insertion complex (CN-M-CH3), while the end-on and side-on complexes (M←NCCH3 and M-η2-(NC)-CH3) are also trapped in the matrix. The CCN antisymmetric stretching mode for Ce-η2-(NC)-CH3 was observed at 1536.9 cm-1, which is much lower than the same modes observed for other lanthanides. NBO analysis reveals that Ce exhibits a remarkable 4f-orbital contribution in bonding to N and to C, reconfirming an active 4f-orbital contribution of cerium in bonding in the side-on complex, while the 4f contributions of Sm and Eu to the M-N and M-C bonds are much lower and the 4f orbital of Lu is not involved in bonding.