Peroxosolvates: Formation Criteria, H2O2 Hydrogen Bonding, and Isomorphism with the Corresponding Hydrates

The Cambridge Structural Database has been used to investigate the detailed environment of H2O2 molecules and hydrogen-bond patterns within true peroxosolvates in which the H2O2 molecules do not interact directly with the metal atoms. A study of 65 crystal structures and over 260 hydrogen bonds reveals that H2O2 always forms two H bonds as proton donors and up to four H-bonds as a proton acceptor, but the latter can be absent altogether. The necessary features of peroxosolvate coformers are clarified. (1) Co-formers should not participate in redox reactions with H2O2 and should not catalyze its decomposition. (2) Coformers should be Bronsted bases or exhibit amphoteric properties. The efficiency of the proposed criteria for peroxosolvate formation is illustrated by the synthesis and characterization of several new crystals. Conditions preventing the H2O2/H2O isomorphous substitution are essential for peroxosolvate stability: (1) Every H2O2 in the peroxosolvate has to participate in five or six hydrogen bonds. (2) The distance between the two proton acceptors forming H-bonds with the H2O2 molecule should be longer than the distance defined by the nature of the acceptor atoms.