Polymorph IV of 4-amino-N-2-pyridinylbenzenesulfonamide (sulfapyridine).

C11H11N3O2S, Mr = 249.3, monoclinic, P2(1)/c, a = 13.56 (4), b = 6.48 (1), c = 14.12 (3) A, beta = 113.7 (1) degrees, V = 1136.4 (44) A3, Z = 4, D chi = 1.457 g cm-3, lambda(Mo K alpha) = 0.70926 A, mu = 2.29 cm-1, F(000) = 520, T = 291 K, final R = 0.085 for 1287 independent observed reflections. Sulfapyridine is a sulfonamide drug with antibacterial, antithyroid and antidiabetic properties. The molecule exhibits the same conformation as in all except one of the polymorphs previously studied, despite a hydrogen-bonded packing mode which differs from that observed in the three earlier reported polymorphs. Form IV exhibits three hydrogen bonds of the type N...N = 2.91 (1) A and N...O = 3.007 (7) and 3.076 (7) A.