Do single-electron lithium bonds exist? Prediction and characterization of the $H3C⋯Li–Y$ (⁠$Y=H$⁠, F, OH, CN, NC, and CCH) complexes Available to Purchase

A new kind of single-electron lithium bonding complexes $H3C⋯LiY$ (⁠$Y=H$⁠, F, OH, CN, NC, and CCH) was predicted and characterized in the present paper. Their geometries $(C3v)$ with all real harmonic vibrational frequencies were obtained at the MP2/aug-cc-pVTZ level. For each $H3C⋯LiY$ complex, single-electron Li bond is formed between the unpaired electron of $CH3$ radical and positively charged Li atom of $LiY$ molecule. Due to the formation of the single-electron Li bond, the C–H bonds of the $CH3$ radical bend opposite to the $LiY$ molecule and the $Li–Y$ bond elongates. Abnormally, the three $H3C⋯LiY$ (⁠$Y=CN$⁠, NC, and CCH) complexes exhibit blueshifted $Li–Y$ stretching frequencies along with the elongated $Li–Y$ bonds. Natural bond orbital analyses suggest ca. 0.02 electron transfer from the methyl radical $(CH3)$ to the $LiY$ moiety. In the single occupied molecular orbitals of the $H3C⋯LiY$ complexes, it is also seen that the electron could of the $CH3$ radical approaches the Li atom. The single-electron Li bond energies are $5.20–6.94kcal∕mol$ for the $H3C⋯LiY$ complexes at the $CCSD(T)∕aug-cc-pVDZ+BF$ (bond functions) level with counterpoise procedure. By comparisons with some related systems, it is concluded that the single-electron Li bonds are stronger than single-electron H bonds, and weaker than conventional Li bonds and $π-Li$ bonds.