| Summary: | The hit compound 1,2,4-triazolo[4’,3’:2,3]pyridazino[4,5-<i>b</i>]indole <b>3</b> was synthesized from the reflux of 4-amino-5-indolyl-1,2,4-triazole-3-thione <b>1</b> with 4′-bromoacetophenone <b>2</b> in methanol catalyzed by concentrated HCl and the desired final molecule was obtained by recrystallization from methanol. The suggested structures of compounds <b>1</b> and <b>3</b> based on the spectral characterizations were confirmed by X-ray single crystal diffraction analysis. Compound <b>3</b> crystallized in the triclinic crystal system and <i>P-1</i> space group with <i>a</i> = 5.9308(2) Å, <i>b</i> = 10.9695(3) Å, <i>c</i> = 14.7966(4) Å, <i>α</i> = 100.5010(10)°, <i>β</i> = 98.6180(10)°, and <i>γ</i> = 103.8180(10)°. On the other hand, the crystal system of <b>1</b> is monoclinic, where <i>a</i> = 6.23510(10) Å, <i>b</i> = 26.0156(4) Å, <i>c</i> = 12.4864(2) Å, <i>β</i> = 93.243(2)° and the space group is <i>P2<b><sub>1</sub></b></i>. The triazole and indole rings are found twisted from each other in both compounds. The twist angle is higher in <b>3</b> (12.65°) than <b>1</b> (4.94–7.22°). In the case of the former, the H…H (39.6%), H…C (22.0%), N…H (12.8%) and Br…H (13.2%) contacts are the most dominant while the C…C, C…H, Br…H, N…H and S…S contacts have the characteristics of strong interactions. In the latter, the C…H, N…H, S…H, S…S, and C…C contacts are the most important. In this case, the percentages of the H…H, C…H, N…H and S…H contacts are in the range of 34.9–37.4, 20.5–24.0, 12.2–13.6, 14.0–15.8, respectively. In both systems, the shape index and curvedness of surfaces confirmed the presence of π–π stacking interactions.
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