We do not answer questions directly on this forum: we like you to put some work in first!
What is the structure of MeLi in the solid state? [Be ready for a surprise.] It has the same
structure in hexanes, and in the coordinating solvents Et2O and THF.
You might read about the bonding in B2H6 (diborane: Wikipedia). What do you know about
Fajan's Rules? And in particular their application to Li^+.