Lithiation of M-C₂H₂ results significant enhancement of second-hyperpolarizability. The negatively polarized π-surface of C₂Li₂ raises the molecular orbital energies which strongly favours both metal-HOMO to ligand-LUMO and ligand-HOMO to metal-LUMO charge transfer interactions. Due to the push electron effect by C₂Li₂, the outermost ‘ns’ orbital of alkaline earth metal cannot induce charge transfer instead forms the excess diffuse electron density localized over the alkaline earth metal. Calculated vertical ionization energy of M-C₂Li₂ complexes are smaller than the corresponding isolated metals. CCSD calculated static and dynamic second-hyperpolarizabilities of M-C₂Li₂ complexes are many times larger than that of the corresponding M-C₂H₂ complexes.

MC ₂ H _2的锂化导致第二超极化率显着提高。C ₂ Li ₂的负极化π表面提高了分子轨道的能量，这极大地促进了金属-HOMO与配体-LUMO以及配体-HOMO与金属-LUMO电荷转移的相互作用。由于C ₂ Li ₂的推动电子效应，碱土金属的最外面的“ ns ”轨道不能引起电荷转移，而是形成了位于碱土金属上的过量扩散电子密度。计算出的MC ₂ Li _2的垂直电离能配合物小于相应的分离金属。CCSD计算得出的MC ₂ Li ₂配合物的静态和动态第二超极化率是相应MC ₂ H ₂配合物的静态和动态第二超极化率的许多倍。