POLYMORPHS OF NITROFURANTOIN .2. PREPARATION AND X-RAY CRYSTAL-STRUCTURES OF 2 ANHYDROUS FORMS OF NITROFURANTOIN

The preparation and X-ray crystal structures of two polymorphs of the antibacterial drug nitrofurantoin are reported. The alpha-polymorph is triclinic, space group P1BAR with a = 6.774(l), b = 7.795(1), c = 9.8 03(2) angstrom, alpha = 106.68(1), beta = 104.09(2), gamma = 92.29(1)- degrees, Z = 2. The beta-polymorph is monoclinic, space group P2(1)/n with a = 7.840(5), b = 6.486(l), c = 18.911(6) angstrom, beta = 93.17( 3)-degrees, 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.