Crystal structures of the dimethyl sulfoxide solvate of 3,6-bis(indol-3-yl)-1,4-dimethylpiperazine-2,5-dione and of the dimethyl sulfoxide and tetrahydrofuran solvates of 1,4-dimethyl-3,6-bis(2-methylindol-3-yl)piperazine-2,5-dione

The syntheses and structures of the dimethyl sulfoxide (DMSO) solvate of 3,6-bis(indol-3-yl)-1,4-dimethylpiperazine-2,5-dione, C11H10N2O (I), and of the dimethyl sulfoxide and tetrahydrofuran (THF) solvates of 1,4-dimethyl-3,6-bis(2-methylindol-3-yl)piperazine-2,5-dione, C12H12N2O, (II) and (III), respectively, are reported. The asymmetric units of (I) and (II) each contain two crystallographically independent half-molecules that are completed by inversion symmetry, whereas (III) contains one independent half-molecule. In all three structures, the piperazine-2,5-dione core is essentially planar and the overall molecular non-planarity arises from rotations of the indole substituents: ranging between 58 and 63° in (I), approximately 72° for both independent molecules in (II) and approximately 62° in (III). In the crystal of (I), molecules are linked by two N - H⋯O hydrogen bonds to form C(18) chains; (II) features a single N - H⋯O contact giving C(8) chains; and (III) exhibits N - H⋯O interactions that generate C(7) chains assembling into sheets lying parallel to (100). No significant π-π stacking is present in any of these structures. All three structures contain regions of disordered solvent (DMSO or THF) that were treated with a solvent mask during refinement.