Insight into the nature of the interactions of pyridine, funan and thiophene with LiNH2

The optimizations geometries and the intermolecular interactions between C5H5N and C4H4Y(Y = O, S) with LiNH2 have been investigated with the MP2 method and various density functional theory (DFT) including B3LYP, M06 and M06-2X. After comparing the results using the benchmark CCSD(T)/aug-cc-pVDZ approach we found that the M06 and B3LYP functionals provided the accurate and reliable results for the lithium bond. The results revealed that the complexes of C5H5N have only σ-type lithium bond complexes. The complexes of C4H4O have σ-type and π-type lithium bond complexes, while the complexes of C4H4S have only π-type lithium bond complexes. The Li–N stretch vibration has a red shift in the σ-type lithium bond complexes. However, it exhibits a blue shift in the π-type lithium bond complexes. The nature of lithium bond has been analyzed with natural bond orbital (NBO), atoms in molecules (AIMs) and symmetry adapted perturbation theory (SAPT) methods. The results indicate that σ-type lithium bond complexes interactions are predominantly electrostatic in nature, while the induction forces dominate the π-type lithium bond complexes.