Physicochemical and structural studies of triamterene.

It has been shown by several physicochemical techniques that the existence of different crystal forms of triamterene, as well as the crystalline products from different solvents with distinct differences in melting points, does not necessarily imply polymorphic crystal forms. The crystalline structure for triamterene is reported herein, revealing a N,N-dimethylformamide molecule and a water molecule within the crystal lattice. Triamterene crystallizes in a face-centered orthorhombic space group, Fdd2 (#43), when grown from aqueous solutions of dimethylformamide (N,N-DMF). In addition, the asymmetric unit contains a partially occupied molecule which is situated on a crystallographic twofold axis. Weak hydrogen bonding occurs between atoms O(1) and N(7), with a distance of 2.66 A, O(1) and N(5) with a distance of 2.96 A, O(2) and N(1), at two different symmetry sites of 2.99 A, and N(2) and N(7), with a distance of 2.91 A. The different solvated crystalline triamterene specimens have different melting points depending on organic solvation, water, or both.