CO Activation on the Late Lanthanide Dimers:  Matrix Infrared Spectra of the Ln₂[η²(μ₂-C, O)]_x (Ln = Tb, Dy, Ho, Er, Lu; x = 1, 2) Molecules

Reactions of laser-ablated late lanthanide atoms (Tb, Dy, Ho, Er, Tm, Yb, and Lu) with dilute carbon monoxide molecules in solid argon have been investigated using matrix-isolation infrared spectroscopy. The Ln₂[η²(μ₂-C, O)]_x (Ln = Tb, Dy, Ho, Er, Lu; x = 1, 2) molecules are observed upon sample annealing, whereas no product is observed for Tm and Yb. The C−O stretching frequencies in these dilanthanide carbonyls range from 1100 to 1300 cm^-1, far below the value of free CO in the gas phase (2143.5 cm^-1), implying that the C−O bonds are highly activated. Density functional theory calculations have been performed on these products. These Ln₂[η²(μ₂-C, O)]_x molecules are predicted to have planar structures, which carry asymmetrically bridging CO moieties that are tilted to the side.