Trigonal-Bipyramidal vs. Octahedral Coordination in Indium(III) Complexes with Potentially S,N,S-Tridentate Thiosemicarbazones

Three bis-chelates of indium(III) with (partially fluorinated) S,N,S-tridentate thiosemicarbazones (H2L) were prepared and their structures were studied in solution and in the solid state by NMR, ESI MS and single-crystal X-ray diffraction. The three compounds are isostructural in solution with five-coordinate In-III ions and two differently coordinated thiosemicarbazonato ligands, [In(L)(HL)]. A temperature-dependent H-1 NMR study reflects the presence of dynamic processes in the molecules such as the resolution of hindered rotation around CN bonds with partial double-bond character and the pH-triggered isomerization between 5- and 6-coordinate species. The latter is confirmed by the isolation of compounds with different solid-state structures, [In(L)(HL)] and [In(L)(2)](-), depending on fluorine-substitutions in the periphery of the thiosemicarbazones.