Anab initioinvestigation of alkali-metal non-covalent bonds BMIDLINE HORIZONTAL ELLIPSISLiR and BMIDLINE HORIZONTAL ELLIPSISNaR (R = F, H or CH3) formed with simple Lewis bases B: the relative inductive effects of F, H and CH3

The alkali-metal bonds formed by simple molecules LiR and NaR (R = F, H or CH3) with each of the six Lewis bases B = OC, HCN, H2O, H3N, H2S and H3P were investigated byab initiocalculations at the CCSD(T)/AVTZ and CCSD(T)/awCVTZ levels of theory with the aim of characterising this type of non-covalent interaction. In some complexes, two minima were discovered, especially for those involving the NaR. The higher-energy minimum (referred to as Type I) for a given B was found to have geometry that is isomorphous with that of the corresponding hydrogen-bonded analogue BMIDLINE HORIZONTAL ELLIPSISHF. The lower-energy minimum (when two were present) showed evidence of a significant secondary interaction of R with the main electrophilic region of B (Type II complexes). EnergiesDCBSe for dissociation of the complexes into separate components were found to be directly proportional to the intermolecular stretching force constantksigmaThe value ofDCBSe could be partitioned into a nucleophilicity of B and an electrophilicity of LiR or NaR, with the orderELiHgreater than or similar to ELiF=ELiCH3for the LiR andENaF>ENaHapproximate to ENaCH3for the NaR. For a given B, the order of the electrophilicities isELiR>ENaR, which presumably reflects the fact that Li+is smaller than Na+and can approach the Lewis base more closely. A SAPT analysis revealed that the complexes BMIDLINE HORIZONTAL ELLIPSISLiR and BMIDLINE HORIZONTAL ELLIPSISNaR have larger electrostatic contributions toDethan do the hydrogen- and halogen-bonded counterparts BMIDLINE HORIZONTAL ELLIPSISHCl and BMIDLINE HORIZONTAL ELLIPSISClF.