A second orthorhombic polymorph of (Z)-3-(9-anthryl)-1-(2-thienyl)prop-2-en-1-one

The title heteroaryl chalcone, C21H14OS, is a second orthorhombic polymorph which crystallizes in the space group P212121. The structure was previously reported [Fun et al. (2009 ▶). Acta Cryst. E65, o2168-o2169] in the space group Pna21. The bond distances and angles are similar in both structures. In contrast, the overall crystal packing is different from that in the first orthorhombic Pna21 polymorph in which molecules were stacked into columns along the b axis and the thiophene units of two adjacent columns were stacked in a head to tail fashion. In the present polymorph, molecules are found to dimerize through a weak S⋯S interaction [3.6513 (7) Å] and these dimers are arranged into sheets parallel to the bc plane. There are no classical hydrogen bonds in the packing which features short C⋯O [3.2832 (2)–3.6251 (9) Å], C⋯S [3.4879 (17)–3.6251 (19) Å] and S⋯O [2.9948 (16) Å] contacts, together with C—H⋯π interactions. Similar contacts were found in the other polymorph.

The title heteroaryl chalcone, C 21 H 14 OS, is a second orthorhombic polymorph which crystallizes in the space group P2 1 2 1 2 1 . The structure was previously reported . Acta Cryst. E65, o2168-o2169] in the space group Pna2 1 . The bond distances and angles are similar in both structures. In contrast, the overall crystal packing is different from that in the first orthorhombic Pna2 1 polymorph in which molecules were stacked into columns along the b axis and the thiophene units of two adjacent columns were stacked in a head to tail fashion. In the present polymorph, molecules are found to dimerize through a weak SÁ Á ÁS interaction [3.6513 (7) Å ] and these dimers are arranged into sheets parallel to the bc plane. There are no classical hydrogen bonds in the packing which features short CÁ Á ÁO [3.2832 (2)-3.6251 (9) Å ], CÁ Á ÁS [3.4879 (17)-3.6251 (19) Å ] and SÁ Á ÁO [2.9948 (16) Å ] contacts, together with C-HÁ Á Á interactions. Similar contacts were found in the other polymorph.
In the crystal packing ( Fig. 2), molecules are found to dimerize through a non-bonding S···S interaction [S···S = 3.6513 (7) Å]. The dimers are arranged into sheets parallel to the bc plane. These sheets are stacked along the a axis. The intermolecular interactions and short contacts are almost similar in both polymorph. There is no classic hydrogen bond and the crystal is consolidated by short C···O [3.2832 (2)-3.6251 (9)  contacts, as well as C-H···π interactions (Table 1); Cg 1 , Cg 2 and Cg 3 are the centroids of the S1/C18-C21, C1-C6 and C8-C13 rings, respectively.

Experimental
The title compound was synthesized as reported by Fun et al. (2009). Yellow block-shaped single crystals of the title compound suitable for x-ray structure determination were recrystallized from ethanol/acetone (1:1 v/v) by slow evaporation of the solvent at room temperature over several days, Mp. 400-401 K.

Refinement
The H atom attached to C19 was placed in a calculated position, with d(C-H) = 0.93 Å, U iso = 1.2U eq (C). The remaining H atoms were located from the difference maps and refined isotropically. The highest residual electron density peak is located at 0.04 Å from C19 and the deepest hole is 0.07 Å from C20. A total of 1830 Friedel pairs were used to determine the absolute configuration. Fig. 1. The molecular structure of the title compound, showing 50% probability displacement ellipsoids and the atom-numbering scheme.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 120.0 (1) K. as those based on F, and R-factors based on ALL data will be even larger.