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-di-methyl-piperazine-2,5-dione, C₁₁H₁₀N₂O (<b>I</b>), and of the dimethyl sulfoxide and tetra-hydro-furan (THF) solvates of 1,4-dimethyl-3,6-bis-(2-methyl-indol-3-yl)piperazine-2,5-dione, C₁₂H₁₂N₂O, (<b>II</b>) and (<b>III</b>), respectively, are reported. The asymmetric units of (<b>I</b>) and (<b>II</b>) each contain two crystallographically independent half-mol-ecules that are completed by inversion symmetry, whereas (<b>III</b>) contains one independent half-mol-ecule. In all three structures, the piperazine-2,5-dione core is essentially planar and the overall mol-ecular non-planarity arises from rotations of the indole substituents: ranging between 58 and 63° in (<b>I</b>), approximately 72° for both independent mol-ecules in (<b>II</b>) and approximately 62° in (<b>III</b>). In the crystal of (<b>I</b>), mol-ecules are linked by two N-H⋯O hydrogen bonds to form <i>C</i>(18) chains; (<b>II</b>) features a single N-H⋯O contact giving <i>C</i>(8) chains; and (<b>III</b>) exhibits N-H⋯O inter-actions that generate <i>C</i>(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.