Reactions between Li Atoms and RCN (R = H or CH3): Semiempirical SCF MO and Matrix Isolation ESR Studies

Reaction passage between the Li atom and the HCN molecule and that between the Li atom and the CH 3 CN molecule were examined by a semiempirical molecular orbital method (MNDO). For both systems two distinct passages were revealed; one leads to the formation of an end-on complex ( I ), HCN···Li, and the other to the formation of a side-on complex ( II ), Li + (HCN) - . The end-on complex is a weak, van der Waals type, while the side-on complex is a strong, charge-transferred type as indicated. An ESR study of argon matrices in which Li atoms and HCN (or CH 3 CN) had been co-condensed revealed the presence of the two complexes in accord with the theoretical prediction. Irradiation of the matrix with near-IR light (λ = 850 ± 50 nm) resulted in conversion of complex I to complex II . The g tensors and the hyperfine coupling tensors of the linear and side-on complexes observed in both the Li/HCN and Li/CH 3 CN systems were determined. In complex I the unpaired electron is in an sp hybridized orbital of Li projected away from the ligand. In complex II, the unpaired electron is essentially in the in-plane antibonding π orbital of the C−N moiety.