Two monosodium salt hydrates of Colour Index Pigment Red 48.

We report herein the crystal structures of a monohydrate of Colour Index Pigment Red 48 (P.R.48) (systematic name: monosodium 2-{2-[3-carboxy-2-oxo-1,2-dihydronaphthalen-1-ylidene]hydrazin-1-yl}-4-chloro-5-methylbenzenesulfonate monohydrate), Na+·C18H12ClO6S-·H2O, and a dihydrate, Na+·C18H12ClO6S-·2H2O. The two monosodium salt hydrates of P.R.48 were obtained from in-house synthesized P.R.48. Both have monoclinic (P21/c) symmetry at 173 K. The crystal packing of both crystal structures shows a layer arrangement whereby N-H...O and O-H...O hydrogen bonds are formed.