Structure of 3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazine isethionate solvate (lamotrigine isethionate)

Abstract

The crystal and molecular structure of lamotrigine isethionate, C₉H₈Cl₂N₅ ⁺ .HOC₂H₄SO₃ ⁻ has been determined by direct methods. The compound crystallizes in the tetragonal space group I4₁/a. The isethionate moiety forms multiple hydrogen bonds to the lamotrigine nucleus, three from one isethionate, two from a symmetry related isethionate and a further two from two different symmetry related molecules. Protonation of N(2′) in the triazine ring, not observed in the native lamotrigine structure is presumably associated with the interaction of the isethionate moiety. Both rings in the lamotrigine moiety are essentially planar, with a dihedral angle of 66.08(7)° compared to 80.70° in native lamotrigine. The connecting bond length C(1)—C(6′) = 1.493(3) Å also correlates well with values in related compounds (1.480(3) Å) in the native structures.