A novel expanded fulleride results from the room temperature reaction of Na2C60 with ammonia. The rhombohedral packing of (ND3)(8)Na2C60 arises from cooperative rearrangement of the face-centered cubic structure of the starting material, via a bcc intermediate. The interfulleride distance within the formerly close-packed layers increases to 12.22 Angstrom while 10.24 Angstrom contacts are maintained between the layers, which retain an ABC stacking sequence. A combination of minimized C...D repulsions and attractive N-D...pi interactions between the dynamically reorientating Na(ND3)(4)(+) and C-60(2-) units control the structure.