Solvent-mediated pseudo-quadruple hydrogen-bond motifs in three lamotrigine-carboxylic acid complexes

Lamotrigine, an antiepileptic drug, has been complexed with three aromatic carboxylic acids. All three compounds crystallize with the inclusion of N,N-dimethylformamide (DMF) solvent, viz. lamotriginium [3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazin-2-ium] 4-iodobenzoate N,N-dimethylformamide monosolvate, C9H8Cl2N5(+)·C7H4IO2(-)·C3H7NO, (I), lamotriginium 4-methylbenzoate N,N-dimethylformamide monosolvate, C9H7Cl2N5(+)·C8H8O2(-)·C3H7NO, (II), and lamotriginium 3,5-dinitro-2-hydroxybenzoate N,N-dimethylformamide monosolvate, C9H8Cl2N5(+)·C7H3N2O7(-)·C3H7NO, (III). In all three structures, proton transfer takes place from the acid to the lamotrigine molecule. However, in (I) and (II), the acidic H atom is disordered over two sites and there is only partial transfer of the H atom from O to N. In (III), the corresponding H atom is ordered and complete proton transfer has occurred. Lamotrigine-lamotrigine, lamotrigine-acid and lamotrigine-solvent interactions are observed in all three structures and they thereby exhibit isostructurality. The DMF solvent extends the lamotrigine-lamotrigine dimers into a pseudo-quadruple hydrogen-bonding motif.