English: These are alternative representations of the ammonia borane molecule, written BNH
6 or H
3BNH
3.

Because its central B−N bond is a coordinate covalent bond, ammonia borane can be drawn several ways and its formula can be written (as text) several more ways:
The three forms shown in this image image can be written like this:

• H
  3B←:NH
  3 (or BH
  3←:NH
  3)
• H
  3B←NH
  3 (writes the coordinate covalent single bond as "←")
• H
  3B−
  −N+
  H
  3 (shows the formal charges on the atoms)

And there are a few more:

• H
  3B−NH
  3 (shows the single bond explicitly)
• BH
  3•NH
  3 (adduct style?)
• H
  3N:→BH
  3 (shows the + charge first, matching conventions for salts like the order of the name does) (reversed order from the rest. why not?)

(The ammonia borane molecule does not have any resonance structures.)