The crystal structures of two isomers of 5-(phenyl-iso-thia-zol-yl)-1,3,4-oxa-thia-zol-2-one.

The syntheses and crystal structures of two isomers of phenyl iso­thia­zolyl oxa­thia­zolone, C11H6N2O2S2, are described [systematic names: 5-(3-phenyl­iso­thia­zol-5-yl)-1,3,4-oxa­thia­zol-2-one, (I), and 5-(3-phenyl­iso­thia­zol-4-yl)-1,3,4-oxa­thia­zol-2-one, (II)]. There are two almost planar (r.m.s. deviations = 0.032 and 0.063 A) mol­ecules of isomer (I) in the asymmetric unit, which form centrosymmetric tetra­mers linked by strong S⋯N [3.072 (2) A] and S⋯O contacts [3.089 (1) A]. The tetra­mers are π-stacked parallel to the a-axis direction. The single mol­ecule in the asymmetric unit of isomer (II) is twisted into a non-planar conformation by steric repulsion [dihedral angles between the central iso­thia­zolyl ring and the pendant oxa­thia­zolone and phenyl rings are 13.27 (6) and 61.18 (7)°, respectively], which disrupts the π-conjugation between the heteroaromatic iso­thia­zoloyl ring and the non-aromatic oxa­thia­zolone heterocycle. In the crystal of isomer (II), the strong S⋯O [3.020 (1) A] and S⋯C contacts [3.299 (2) A] and the non-planar structure of the mol­ecule lead to a form of π-stacking not observed in isomer (I) or other oxa­thia­zolone derivatives.