The preparation and X-ray crystal structures of two polymorphs of the antibacterial drug nitrofurantoin are reported. The
-polymorph is triclinic, space group
P¯1 with
a=6.774(1),
b=7.795(1),
c=9.803(2)Å,
=106.68(1),
=104.09(2),
=92.29(1)°,
Z=2. The
-polymorph is monoclinic, space group
P2
1/
n with
a=7.840(5),
b=6.486(1),
c=18.911(6)Å,
=93.17(3)°,
Z=4. The nitrofurantoin molecules adopt the same, planar conformation in both polymorphs. Both crystal structures are built up from layers held together by van der Waals forces. In each polymorph, intralayer cohesion is effected by N-H
O and C-H
O hydrogen bonds, but their arrangements differ in the two crystals. The significance of the C-H
O hydrogen bond, now known to occur in four modifications of nitrofurantoin, is discussed.