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 InIII ions and two differently coordinated thiosemicarbazonato ligands, [In(L)(HL)]. A temperature‐dependent 1H 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. Trifluoromethylation of a thiosemicarbazone ligand affects the coordination number of an indium(III) complex. While a complex with C.N. 5 is observed in solution, a distorted octahedral compound is formed in the solid state.