Understanding microsolvation of Li+: structural and energetical analyses

Abstract

A stochastic exploration of the quantum conformational space for the (H(2)O)(n)Li(+), n = 3, 4, 5 complexes produced 32 molecular clusters at the B3LYP/6-311++G** and MP2/6-311++G** levels. The first solvation shell is predicted to comprise a maximum of 4 water molecules. Energy decomposition analyses were performed to determine the relationship between the geometrical features of the complexes and the types of interactions responsible for their stabilization. Our findings reveal that electrostatic interactions are major players determining the structures and relative stabilities of the clusters. The formal charge on the Li atom leads to two distinct types of hydrogen bonds, scattered in a wide range of distances (1.61-2.32 Å), in many cases affording H-bonds that are considerably larger and considerably shorter than those in pure water clusters (typically ∼1.97 Å).

Microsolvation of Sr2+, Ba2+: Structures, energies, bonding, and nuclear magnetic shieldings

“…according to Gonzalez and coworkers [2], and according to Table 3, up to 314, 241, 201, 175 kcal/mol are obtained for the microsolvation of Mg 2 + , Ca 2+ , Sr 2+ , Ba 2+ , respectively. It is worth noticing that for the doubly charged cations, from a purely energetic point of view, a maximum coordination of the central cation with water molecules is preferred up to n ¼ 6, however, for smaller cations with fewer electrons (Li + , e.g., Romero et al [3]), the electrophilic power is such that even when five or more water molecules are available for microsolvation, a maximum coordination of n ¼ 4 is preferred, the excess solvent molecules attaching to the Li H 2 O ð Þ 4 Â Ã þ cluster via hydrogen bonds in a second solvation shell. Furthermore, weakly bonded clusters are extremely difficult to analyze because their PESs are populated by large numbers of local minima very close in energy, thus, many structures contribute to experimental signals, conversely, in the explicit microsolvation of Sr 2+ , Ba 2+ with up to six water molecules, the electrophilic power of the cations is such that a dominant minimum, corresponding to the maximum coordination of the central cation,…”

Microsolvation of heavy halides

“…Conversely, there does not seem to be much of a difference in the shieldings between the charges in I − , At − . In the same line of reasoning, it is clear that heavy halides exhibit smaller magnitudes in microsolvation energies when compared to other singly charged anions such as F − , for which BE ∈ [−24, −100] kcal/mol (with 1–6 molecules of water), [39] and cations such as Li + , BE ∈ [−62, −115] kcal/mol (with 3–5 molecules of water), [56] and [CH 3 Hg] + , BE ∈ [−32, −65] kcal/mol (with 1–3 molecules of water) [57].…”

Microsolvation of small cations and anions

“…Our results indicate that microsolvation of cations and anions occur via two structurally different arrangements. For generic bare X n + cations (X = Li, Ca, Mg, n = 1, 2), water molecules in the first solvation shell place the oxygen atoms in direct contact with the source of the positive charge, leading to highly ionic X⋯O interactions. Conversely, solute ↔ solvent interactions in the microsolvation of complex cations such as [CH 3 Hg] + is considerably more complicated, affording partially covalent Hg⋯O interactions when only one water molecule is present, furthermore, consideration of additional waters suggest that they microsolvate the [CH 3 Hg⋯OH 2 ] + unit .…”

“…In the particular case of water microsolvation of bare cations [16,17] and anions, [2] as a general rule, two types of intermolecular contacts dictate structural and energetical preferences: on one hand, explicit electrostatic interactions between the formal charge and the polarized ends of water molecules, and, on the other, pure and charge assisted hydrogen bonding among waters. Some complex ions [18][19][20][21][22][23] also allow hydrogen bonding between solute and solvent.…”