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