Aqueous micro-solvation of Li+ ions: Thermodynamics and energetic studies of Li+-(H2O)n (n = 1-6) structures

The structures and thermodynamic parameters of hydrated lithium ion clusters incorporating a single lithium ion and up to six water molecules have been determined with density functional (DFT) and Hartree-Fock (HF) at the RB3LYP/631G(d,p) levels of theory. The possible formed structures are found to be 23 Li+(H2O)n complex for n = 1-6. The primary solvation shell in the gas phase is confirmed to be tetrahydrated in aqueous environment. Very important role of intermolecular hydrogen bond in determining the stability of solvation process of different ions is confirmed by theoretical studies. The calculated gas phase coordination number in the first solvation sphere of a hydrated lithium metal ion is found to be four and the same is also confirmed by the experimental findings. The equilibrium lithium-oxygen distance of 1.970 Å at the present B3LYP level of study is in excellent agreement with the X-ray diffraction result of 1.980 Å and neutron scattering study with a result of 1.90 Å for a tetrahydrated lithium cluster. NBO was analyzed and discussed.