Hydration of lanthanide chloride salts: a quantum chemical and classical molecular dynamics simulation study

We present the results of a quantum chemical and classical molecular dynamics simulation study of some solutions containing chloride salts of La(3+), Gd(3+), and Er(3+) at various concentrations (from 0.05 to 5 M), with the purpose of understanding their structure and dynamics and analyzing how the coordination varies along the lanthanide series. In the La-Cl case, nine water molecules surround the central La(3+) cation in the first solvation shell, and chloride is present only in the second shell for all solutions but the most concentrated one (5 M). In the Gd(3+) case, the coordination number is ∼8.6 for the two lowest concentrations (0.05 and 0.1 M), and then it decreases rapidly. In the Er(3+) case, the coordination number is 7.4 for the two lowest concentrations (0.05 and 0.1 M), and then it decreases. The counterion Cl(-) is not present in the first solvation shell in the La(3+) case for most of the solutions, but it becomes progressively closer to the central cation in the Gd(3+) and Er(3+) cases, even at low concentrations.