Abstract Despite the significance of H 2 O 2 -metal adducts in catalysis, materials science and biotechnology, the nature of the interactions between H 2 O 2 and metal cations remains elusive and debatable. This is primarily due to the extremely weak coordinating ability of H 2 O 2 , which poses challenges in characterizing and understanding the specific nature of these interactions. Herein, we present an approach to obtain H 2 O 2 –metal complexes that employs neat H 2 O 2 as both solvent and ligand. SnCl 4 effectively binds H 2 O 2 , forming a SnCl 4 (H 2 O 2 ) 2 complex, as confirmed by 119 Sn and 17 O NMR spectroscopy. Crystalline adducts, SnCl 4 (H 2 O 2 ) 2 ·H 2 O 2 ·18-crown-6 and 2SnCl 4 (H 2 O 2 )(H 2 O)·18-crown-6, are isolated and characterized by X-ray diffraction, providing the complete characterization of the hydrogen bonding of H 2 O 2 ligands including geometric parameters and energy values. DFT analysis reveals the synergy between a coordinative bond of H 2 O 2 with metal cation and its hydrogen bonding with a second coordination sphere. This synergism of primary and secondary interactions might be a key to understanding H 2 O 2 reactivity in biological systems.