Theoretical prediction characters of unconventional weak bond with carbene as electron donors and Li-Y (YÂ =Â OH, H, F, NC and CN) as electron acceptors

An unconventional lithium bond has been proved to exist in X-C⋯Li-Y(X = H2, F2; Y = OH, H, F, NC and CN) complexes by at MP2/6-311++G(d,p) and MP2/aug-cc-pVTZ levels. The results show that the binding energies for complexes are in the range of −9.30 to −19.98 kcal mol−1 at the CCSD(T)/aug-cc-pVTZ//MP2/aug-cc-pVTZ level. In complexes, the vibration frequencies of Li-Y in Complex-I-IV decreasing and that in Complex-V-VI increasing, suggesting that the Complex-I-IV may be classified as red-shifting lithium bonds complexes and the Complex-V-VI are abnormal blue-shifting complexes. Furthermore, the NBO and AIM were used to unveil the nature of the interaction.