The Key Role of Orbital Interaction in Cooperativity between B⋅⋅⋅N and Hydrogen/Lithium Bonding: An ab initio Study

The aim of this study is to investigate the possible cooperative effects between B⋅⋅⋅N and hydrogen‐ or lithium‐bonding interactions in the ternary H 3 B⋅⋅⋅NCM⋅⋅⋅Z, F 3 B⋅⋅⋅NCM⋅⋅⋅Z and C 5 H 5 B⋅⋅⋅NCM⋅⋅⋅Z complexes, where M=H, Li and Z= NH 3 , N 2 . The characteristic of the interactions in these complexes is studied by molecular electrostatic potential, quantum theory of atoms in molecules and natural bond orbital analyses. For all these complexes, the M⋅⋅⋅N binding distances are always shorter than those in NCM⋅⋅⋅Z binary complexes, which implies that the formation of the B⋅⋅⋅N interaction strengthens the M⋅⋅⋅N bonds. However, unlike H 3 B⋅⋅⋅NCM⋅⋅⋅Z and F 3 B⋅⋅⋅NCM⋅⋅⋅Z complexes, the B⋅⋅⋅N binding distances in C 5 H 5 B⋅⋅⋅NCM⋅⋅⋅Z are found to be longer than those in C 5 H 5 B⋅⋅⋅NCM dimers. Such unusual cooperativity between the B⋅⋅⋅N and hydrogen‐ or lithium‐bonding interactions has not been reported previously. The origin of this unusual cooperativity between B⋅⋅⋅N and M⋅⋅⋅N interactions in C 5 H 5 B⋅⋅⋅NCM⋅⋅⋅Z complexes is explained in term of the back‐bonding π→ π * charge‐transfer between C 5 H 5 B and NCM moieties.