An ab initio study of the properties of some lithium-bonded complexes – Comparison with their hydrogen-bonded analogues. 2. Natural bond orbital and quantum theory of atoms in molecules analysis

A series of lithium-bonded complexes containing lithium fluoride, chloride and bromide and the common bases ammonia, water, phosphine and hydrogen sulphide have been studied by means of ab initio molecular orbital theory. A similar set of complexes, in which the lithium halides were replaced by the hydrogen halides, was also investigated in order to establish the similarities and differences between the corresponding families of complexes. The molecular orbital properties were examined using natural bond orbital (NBO) theory with the object of determining which specific electron donor and acceptor orbitals were involved in each pair of interacting molecules. The electron density topologies were also studied, within the framework of the quantum theory of atoms in molecules (QTAIM), in an effort to ascertain in what ways the electron densities of the isolated monomers responded to the formation of the individual complexes. The parallels between the properties of the two sets of complexes have been described, and the differences traced back to the natures of the constituent monomers.