[Memy]

hello,

is Na a lewis acid that coordinates with a carbonyl oxygen in NABH4 as Li does in LiALH4 ?

In my opinion it does not as LiBH4 lies in between NaBH4 and LiALH4 in its reactivity towards carbonyl compounds and this can be explained by the fact that Li makes the carbonyl C more electrophilic while Na not.

[movies]

Na⁺ is a Lewis acid, but not a very good one.  Li⁺ is a much better Lewis acid and therefore is better at activating carbonyl groups towards reduction.