X-ray powder diffraction, solid-state NMR and dispersion-corrected DFT calculations to investigate the solid state structure of 2-ammonio-5-chloro-4-methylbenzenesulfonate

The title compound, also called CLT acid, is an industrial intermediate in the synthesis of laked red azo pigments for newspaper printing. Solid-state NMR and IR experiments revealed the compound to exist as the zwitterionic tautomer in the solid state. The crystal structure was solved from X-ray powder diffraction data by means of real-space methods using the program DASH 3.1 . Subsequently the structure was refined by the Rietveld method with TOPAS 4.1 . The zwitterionic tautomer gave better confidence values than the non-zwitterionic tautomer. Finally the structure was confirmed by dispersion-corrected density-functional calculations. The compound crystallises in the monoclinic space group Ia , Z = 4 with a = 5.49809(7) Å, b = 32.8051(5) Å, c = 4.92423(7) Å, β = 93.5011(7)° and V = 886.50(2) Å 3 . The molecules form a herringbone pattern with a double layer structure consisting of alternating polar and non-polar layers. Within the polar layers hydrogen bonds and ionic interactions are dominant, whereas the fragments in the non-polar layers are connected by van der Waals interactions.