Crystal Engineering of Organic Salts: Hydrogen-Bonded Supramolecular Motifs in Trimethoprim Sorbate Dihydrate and Trimethoprim o-Nitrobenzoate

Abstract

In the crystal structures of two organic salts, namely, trimethoprim sorbate dihydrate (1) and trimethoprim o-nitrobenzoate (2), the pyrimidine moieties of trimethoprim are protonated at one of the ring nitrogens. In both the compounds, the carboxylate oxygens are hydrogen-bonded to the protonated pyrimidine rings to form the hydrogen-bonded cyclic bimolecular motif. These motifs further self-organize in two different ways to give different types of hydrogen-bonded networks in the two crystal structures. In compound 1, the two inversion related motifs pair through a pair of N−H···N hydrogen bonds involving an unprotonated ring nitrogen and 4-amino group. In addition to this pairing, one of the water oxygens bridges the 2- and 4-amino groups on both sides of pairing to form a complementary DADA (D refers to the hydrogen-bond donor and A refers to the hydrogen-bond acceptor) array of quadruple hydrogen bonds. In compound 2, there is no base-pairing, and the cyclic hydrogen-bonded bimolecular motifs self-assemble into a hydrogen-bonded supramolecular ladder through N−H···O and C−H···O hydrogen bonds. The o-nitrobenzoate ions form a supramolecular chain, the ions being linked by aromatic C−H···O (of the nitro group) hydrogen bonds.