H2SO7

H2SO7 is the chemical formula for a sulfur-oxy acid that would lie beyond the well-known sulfuric acid family. In standard inorganic chemistry, the most familiar related species are sulfuric acid (H2SO4), pyrosulfuric acid or oleum derivatives (H2S2O7), and the various peroxo- and polyoxo-sulfuric acids such as Caro’s acid (H2SO5). H2SO7 is not a widely characterized or routinely isolated compound; in many sources it is treated as a theoretical or transient species that would exist only under highly specific, strongly oxidizing conditions.

If a discrete neutral molecule with formula H2SO7 could be stabilized, its sulfur center would be in an unusually high-oxygen environment. In practice, any real species corresponding to seven oxygens would likely be described in terms of protonation state, peroxo links, or as a transient polyoxo species in solution rather than as a stable, well-defined molecule. Consequently, exact structure, bonding, and oxidation-state assignments are not established in the way they are for H2SO4 or H2SO5.

Properties of H2SO7, where it can be discussed at all, would be dominated by extreme oxidizing power and instability. It would be expected to decompose readily to more stable sulfur-oxygen species, such as H2SO4, or to release oxygen under certain conditions. Because there is little or no widely accepted experimental isolation, practical applications remain nonexistent; discussions of H2SO7 are mainly of theoretical or speculative interest within inorganic chemistry.

See also: sulfuric acid (H2SO4), pyrosulfuric acid (H2S2O7), peroxysulfuric acids (e.g., H2SO5).