Crystal structures of thiazine-indigo pigments, determined from single-crystal and powder diffraction data

Abstract

The crystal structures of two polymorphs of thiazine-indigo, C16H10N2O2S2 were determined by single crystal X-ray diffraction. 7,7′-dimethyl-thiazine-indigo, 7,7′-dimethoxy-thiazine-indigo and 7-monochloro-thiazine-indigo are isostructural to β-thiazine-indigo and 7,7′-dichloro-thiazine-indigo; their structures are refined by Rietveld methods. 7-monochloro-thiazine-indigo shows a head-to-tail-disorder. 6,6′-bis(trifluoromethyl)-thiazine-indigo is not isotypic to any other thiazine-indigo compound. Polymorph screenings were performed; three of the six compounds are polymorphic. In all determined structures the molecules are essentially planar; all molecules are connected by double hydrogen bonds to form parallel chains, but there are three different arrangement of chains. The structures are compared with the chain-structures of other organic pigments like indigo, quinacridone and diketopyrrolopyrrole derivatives.

Crystal structure of disordered nanocrystalline αII-quinacridone determined by electron diffraction

“…in diketopyrrolopyrrole (Pigment Red 254) 25 and thiazine-indigo (Pigment Orange 80). 26 A closer inspection of the crystal structures of the α I and α II -phases of quinacridone reveals that not only the chains, but also the mutual arrangement of the chains within the layers, are almost identical in both phases. The main difference between the polymorphs is the stacking of the layers: either parallel (α I ) or herringbone (α II ).…”