organic chemistry - Structure of Sodium Naphthalenide

This question is a sort of follow-up to my earlier question.

I know about a method of solubilising potassium where the potassium atoms are "trapped" between layers of graphite, but I think that sodium naphthalenide exists only in solution (if a contradiction is found, please inform).

In the solution phase, say in THF, I would expect some THF molecules co-ordinated to the sodium, and an $\eta^4$ complex with naphthalene, involving one ring. An $\eta^{10}$ complex seems possible, involving both the rings, as the negative charge is distributed further, but I haven't read about any $\eta^{10}$ complex. An $\eta^1$ complex might be possible, but the distribution of negative charge will be lesser.

I expect sometehing similar to the tetrahedral form of butyllithium.

What is the structure of sodium naphthalenide?