Microsolvation of lithium iodide dimer studied by ab initio calculations

Ab initio study of hydrated cesium iodide dimer (CsI)2-/0(H2O)0-6 and the cation size effect on (MI)2-/0(H2O)0-6 (M = Li, Na, K, Cs)

The structures of microsolvated (CsI)₂^-/0(H₂O)_0-6 clusters were determined using ab initio calculations. Our studies show that one Cs atom at the apex was firstly separated from the pyramid-shaped (CsI)₂^- unit when the water number reaches 3, whereas CsI distances did not increase significantly from n = 0 to 6 for neutrals. Additionally, the atomic charge and reduced density gradient analyses were carried out; the results reveal that the extra electrons are almost entirely localized on terminal Cs atom and the Cs⁺-water interactions dominate in (CsI)₂^-(H₂O)_0-6. The water-water interactions show up at n = 5. The comparison of (CsI)₂^-/0(H₂O)_n with (MI)₂^-/0(H₂O)_n (M = Li, Na, K) shows that neutral (CsI)₂ is the most difficult to be separated, which matches the law of matching water affinity. As for anions, the most difficult separation occurs in the case of small size (LiI)₂^- due to the effect of extra electrons, and (MI)₂^- with larger size cation is more likely to interact with water to form a pyramid structure.