Theoretical Investigation On The Interaction Of Superatoms Li₃⁺ And Be₁₁ With Water Molecules

Superatom clusters are known for showing properties similar to single atoms in traditional periodic table.Therefore,how superatom clusters interact with other species,as well as their behavior and stability in different molecular environments are meaningful projects.The main contributions of this thesis are as follows:1.the interaction of superalkali cation Li₃⁺with water molecules,as well as the structures and stability of the resulting water complexes have been theoretically studied at the MP2/6-311++G（d,p）level.A great number of geometrical configurations were obtained for the Li₃⁺（H₂O）_n（n=1–5）complexes and Li₃⁺is found to share the same maximum coordination number,namely four,with Li⁺in water clusters.Natural population analysis reveals two main points.First,superalkali Li₃⁺maintains its electronic integrity in the Li₃⁺（H₂O）_n（n=1-4）clusters.Second,the charge distribution of Li₃⁺becomes seriously uneven upon the interaction with five water molecules,so it loses ring conjugation and splits in the lowest-energy isomer of Li₃⁺（H₂O）₅.Localized molecular orbital energy decomposition analysis indicates a dominant contribution of electrostatic interaction to the binding of water molecules to Li₃⁺,which is similar to the case of lithium ion hydrates.However,as the number of water ligands reaches five,the contribution of exchange-repulsion energy exhibits a sharp increase and even exceeds that of the electrostatic term,which proves our assumption that the repulsive effect of water lone-pair electrons on Li₃⁺valence electrons plays an important role in the split of Li₃⁺ring in the Li₃⁺（H₂O）₅ cluster.2.Be₁₁ cluster and multi-valence superatom Al₇^—have the same electronic configuration.Thus,we consider that Be₁₁ may also show multiple valency of+2 and+4 as Al₇^—does.However,according to our previous research on Be_nC and Be_nO cluster systems,Be₁₁C does not show unique stability among the Be_nC clusters,while in the Be_n O series,Be₁₁O exhibits outstanding stability.Thus,it can be concluded that the Be₁₁ cluster tends to exhibit a+2 valence,which makes it a superatom analog of alkaline earth metal atoms.Taking the chemical behavior of alkaline earth metal elements as a reference,we performed a theoretical study on the reaction of Be₁₁ with water molecules.Four complete pathways for H₂ production were obtained that follow either Eley-Rideal（ER）or Langmuir-Hinshelwood（LH）mechanisms.The relative energies of the transition state in all pathways are negative,indicating a high reactivity between Be₁₁ and H₂O.In contrast,it has been reported that Al₇^—exhibits minimal reactivity with H₂O in low-pressure experiments.Therefore,although two metal clusters share the same electronic configuration,their chemical character might be different since the reactivity of a cluster is also related to its geometry and active-site distribution.