The Sodium Anion Is Strongly Perturbed in the Condensed Phase Even Though It Appears Like a Free Ion in Nuclear Magnetic Resonance Experiments.

Solvated sodium anions (Na-) were thought to behave essentially like isolated gas-phase ions that interact only weakly with their environments. For example, 23Na NMR signals for solvated Na- are very sharp, despite the potential for strong quadrupolar broadening. The sharp NMR signals appear to indicate a nearly spherical electron density of the ion. For the present study, ab initio molecular dynamics simulations and quadrupolar relaxation rate calculations were carried out for the Na-/Na+ [2.2.2]cryptand system solvated in methylamine, followed by detailed analyses of the electric field gradient at the sodium nuclei. It is found that Na- does not behave like a quasi-free ion interacting only weakly with its environment. Rather, the filled 3s shell of Na- interacts weakly with the ion's own core and the nucleus, causing Na- to appear in NMR experiments like a free ion.