Revisiting Lanthanide Solvation: The “Gadolinium Break” That Does Exist

Lanthanides (Ln) offer rich and otherwise unusual chemistry, which includes their redox behavior, ligand coordination, diverse quantum phenomena, etc. Unlike the lighter elements, these f-block elements could exhibit nonlinear trends in various chemical and physical properties across the series with a noticeable break often being observed in the central atom gadolinium (Gd). This popular notion of <i>"Gd break"</i> has been challenged and banished by researchers in the past, making this as an ever-debated issue in the chemical fraternity. In this Letter, we examine the solvation behavior of dilute solutions of chlorides of La³⁺, Nd³⁺, Gd³⁺, Ho³⁺, and Lu³⁺ using THz time domain and frequency domain spectroscopy coupled with MD simulation measurements. We find that unlike mono- and divalent cations Ln^III solvation is nonmonotonic and shows a sudden break at Gd. Our result finds relevance considering the fact that with the surge of technological advancement heavy cations are being exposed to the environment, and to understand their potential effect on the flora and fauna, it is a prerequisite to understand their solvation behavior in greater detail.