Matrix Infrared Spectra of Manganese and Iron Isocyanide Complexes

Mono and diisocyanide complexes of manganese and iron were prepared via the reactions of laser-ablated manganese and iron atoms with (CN)₂ in an argon matrix. Product identifications were performed based on the characteristic infrared absorptions from isotopically labeled (CN)₂ experiments as compared with computed values for both cyanides and isocyanides. Manganese atoms reacted with (CN)₂ to produce Mn­(NC)₂ upon λ > 220 nm irradiation, during which MnNC was formed mainly as a result of the photoinduced decomposition of Mn­(NC)₂. Similar reaction products FeNC and Fe­(NC)₂ were formed during the reactions of Fe and (CN)₂. All the product molecules together with the unobserved cyanide isomers were predicted to have linear geometries at the B3LYP level of theory. The cyanide complexes of manganese and iron were computed to be more stable than the isocyanide isomers with energy differences between 0.4 and 4 kcal/mol at the CCSD­(T) level. Although manganese and iron cyanide molecules are slightly more stable according to the theory, no absorption can be assigned to these isomers in the region above the isocyanides possibly due to their low infrared intensities.