Pseudo-polymorphism and crystal engineering: hydrogen-bonded supramolecular networks in trimethoprim m-chlorobenzoate and trimethoprim m-chlorobenzoate dihydrate

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Abstract
This manuscript deals with the crystal structures of two pseudo-polymorphic forms, namely, trimethoprim m-chlorobenzoate (1) and trimethoprim m-chlorobenzoate dihydrate (2). In both the structures, the pyrimidine moieties of trimethoprim are protonated at one of the ring nitrogens. In both the forms, the carboxylate group interacts with the protonated pyrimidine ring to form the cyclic hydrogen-bonded bimolecular motif. These motifs are further self-organized into two different hydrogen-bonded networks. In compound 1, two of the centrosymmetrically-related motifs are hydrogen-bonded to give a complementary DDAA (D refers to the hydrogen bond donor and A refers to the hydrogen bond acceptor) array of quadruple hydrogen bonding pattern. In compound 2, two of the inversion-related motifs are paired through a pair of N–HN hydrogen bonds involving the 2-amino group and the N3 atom. In addition to the pairing, one water molecule bridges the 4-amino group of one motif and the carboxylate oxygen of another motif on both sides of the pairing, leading to a complementary linear array of hydrogen bonds.

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