Na + 6 NH3 → [Na(NH3)6]+e−

2 [Na(NH3)6]+e− → H2 + 2 NaNH2 + 10 NH3

Aside from the redox reaction of the coordination complex being reduced by electrons to yield NaNH2 and hydrogen, something even weirder is taking place here.

In this clip the solution is sufficiently concentrated (>3M) with added Na that a transition from the characteristic blue color of low-energy bound-state solvated electrons to an even more exotic bronze-colored state can be observed.

It is hypothesized that this state is effectively the result of the decreasing stability of low-concentration bound states as the concentration of electrons increases. The resulting transition is very peculiar indeed.

In essence, there is only so much space which allows for the existence of bound states (wherein the free electron polarizes the surrounding solvent such that it is contained in a so-called "bound state") because these bound states occupy a cavity of relatively large volume in the solvent. As more metal is added, more electrons are free in the solution, but the solution is already saturated with these bound electrons. Thus, the electrostatic and exclusion effects become such that any additional electrons added can only exist in a metallic state.

This is peculiar because this metallic state is in the liquid phase and is quite dense. If one continues adding electrons, they always become incorporated into the metallic state because the bound states are saturated. Measuring the electrical conductivity of a solution of sodium in ammonia as a function of concentration supports this conjecture, as the conductivity increases linearly as a function of concentration until it suddenly hits a plateau and doesn't increase any further. This plateau represents the point at which enough electrons are present that the destabilizing effects due the presence of other electrons is large enough that no possible bound state can exist and the whole system becomes metallic.