Hydrogen bond enhanced coordination of hydrogen peroxide to indium trichloride

Coordination of hydrogen peroxide by a metal center is the first step in the enzymatic cycle of peroxidases and catalases. Although this process occurs readily in living cells, synthesizing molecular complexes with the H₂O₂ ligand remains challenging due to hydrogen peroxide's weaker coordinating ability compared to other polar solvents. To date, structural information on coordination compounds with hydrogen peroxide as a ligand is represented by the crystal structures of a zinc complex and two tin complexes. This work demonstrates that hydrogen peroxide complexes can be prepared from coordinatively saturated compounds, such as indium(III) chloride. Ether compounds like 18-crown-6 or diethyl ether dissolve InCl₃, enabling its interaction with H₂O₂. Three InCl₃ complexes with hydrogen peroxide ligand, [InCl₃(H₂O)₂(H₂O₂)]·18-crown-6, [InCl₂(18-crown-6)][(H₂O₂)InCl₄] and [fac-InCl₃(H₂O₂)_0.5(H₂O)_0.5(18-crown-6)], were isolated under different conditions, presenting a valuable addition to a very small family of structurally characterized H₂O₂ complexes. The crystal structures of these complexes were characterized by single-crystal X-ray diffraction analysis. DFT calculations unveiled the key role of the hydrogen bonding of the H₂O₂ ligand with ether molecules enhancing hydrogen peroxide coordination to In(III) center. Variable-temperature ¹H NMR data support the κ¹-coordination of H₂O₂ with InCl₃ in ethereal solution.