Infrared Spectroscopic and Theoretical Studies of Group 3 Metal Isocyanide Molecules

A series of group 3 metal isocyanide complexes were prepared via the reactions of laser ablated scandium, yttrium, and lanthanum atoms with (CN)₂ in an argon matrix. The product structures were identified on the basis of their characteristic infrared absorptions from isotopically labeled (CN)₂ samples as well as the calculated frequencies and isotopic frequency ratios. Group 3 metal atoms reacted with (CN)₂ to form M(NC)₂ (M = Sc, Y, La) when the samples were subjected to λ > 220 nm irradiation. Other products such as M(NC)₃ and MNC were produced together with M(NC)₂ through either the reactions of M(NC)₂ and (CN)₂ or the loss of one CN ligand from M(NC)₂. CCSD(T)//B3LYP calculations reveal that ScNC possesses a ³Δ ground state, while ¹Σ⁺ is most stable for YNC and LaNC. All of the M(NC)₂ and M(NC)₃ complexes were predicted to have doublet and singlet ground states, respectively. Group 3 metal cyanides are less stable than the isocyanides by at least 4 kcal/mol at the CCSD(T) level, and their C-N stretches are much weaker than the N-C stretches of the isocyanides. No absorption can be assigned to the M(CN) _x complex, which would appear between 2100 and 2250 cm^-1.