Key indicators: single-crystal X-ray study; T = 100 K; mean (C-C) = 0.003 Å; R factor = 0.033; wR factor = 0.090; data-to-parameter ratio = 16.6.The asymmetric unit of the title cyclic thiourea derivative, C 10 H 12 N 2 S, comprises two molecules, each of which has a twist about the CH 2 -CH 2 bond within the five-membered ring. The major difference between the independent molecules is manifested in the relative orientations of the five-and sixmembered rings [dihedral angles between the least-squares planes = 28.03 (11) and 41.54 (11) ]. A network of C-HÁ Á Á interactions consolidates the three-dimensional crystal packing.

The crystal and molecular structure of a second polymorph (P2 1 /n) of [1,4-ROC( = S)N(H)C( = O)C 6 H 4 C( = O) N(H)C( = S)OR], R = Et, is shown to have inversion symmetry and to have a more twisted conformation than the previously reported P4 3 2 1 2 form which has 2-fold symmetry. Despite utilising equivalent atoms in forming intermolecular interactions, very distinct crystal packing patterns are observed. Crystal characteristics and theory (DFT) are consistent with the P4 3 2 1 2 form being more stable, a conclusion correlated with the observation that this form is the overwhelming majority of the sample (PXRD). An analysis of a binuclear copper(I) complex containing the R = iPr analogue, reveals the neutral ligand to bind via the thione-S atom resulting in a distorted ClP 2 S tetrahedral geometry.