Three novel compounds of 5-trifluoromethoxy-1H-indole-2,3-dione 3-thiosemicarbazone: Synthesis, crystal structures and molecular interactions

5-Trifluoromethoxy-1H-indole-2,3-dione 3-(N-ethyl/benzylthiosemicarbazone) (2a/2b) and 5-trifluoromethoxy-1-morpholinomethyl-1H-indole-2,3-dione 3-(N-ethylthiosemicarbazone) (3a) were synthesized. The structures of the compounds were confirmed by elemental analysis, spectral data and X-ray single crystal diffraction analysis. The morpholin ring which adopts chair conformation and ethylamino group of 3a are disordered over two sets of sites with unequal occupancy. The indole heterocycle is nearly planar and the dihedral angle between the pyrrole and the adjacent phenyl ring is 2.09° (in 2a), 4.61° (in 2b) and 2.16° (in 3a). In all three crystal structures, a strong N-HO hydrogen bond links the flat conjugated H-N-N=C-C=O fragment into a six-membered ring. The molecules 2a, 2b and 3a have potential groups of proton donors (thiosemicarbazone group) available for hydrogen bonding. The structures 2b and 3a consist of isolated molecules, while that of 2a contains dimers formed by C-HO hydrogen bonds. The molecules are linked into three dimensional framework structure by a combination of mainly N-HN and N-HO hydrogen bonds and weak C-Fπ and ππ interactions.