Hydrogen bonding patterns in 3,5-diamino-6-aryl triazines

The crystal structure of two related 1,2,4-triazine derivatives, C9H7N5Cl2. H2O (1) and C12H14N5Cl2+. CH3SO3-.H2O (2) that have different biological ef fects, have been determined. Lamotrigine (Lamictal, 1) is a novel anticonvu lsant and BWA256C (2) is a class I antiarrythmic drug. The dihedral angles between the least-squares planes of almost exactly planar phenyl and triazi ne rings are 76.42(6) and 76.08(6)degrees, for compounds I and 2, respectiv ely. In 2, protonation takes place at the iminium nitrogen atom, thus sugge sting the importance of resonance through the triazine ring. This resonance is also confirmed by the pattern of bond lengths and angles. Extensive net works of hydrogen bonds, in which all molecular species are involved, rule the crystal packing in both compounds. The analysis of hydrogen bond networ ks in other 3,5-diamino-6-aryl derivatives suggests that there is a strong influence of co-crystallizing solvent molecule on the nature of resulting h ydrogen bond topology. (C) 2001 Elsevier Science B.V. All rights reserved.