Disodium di­hydrogen 1,2,4,5-benzene­tetra­carboxyl­ate dihydrate

Each of the two acid H atoms in the centrosymmetric [C₆H₂(CO₂H)₂(CO₂)₂]²⁻ dianion of disodium di­hydrogen 1,2,4,5-benzene­tetra­carboxyl­ate dihydrate, 2Na⁺·C₁₀H₄O₈²⁻·2H₂O, holds together a pair of adjacent carboxyl groups so that all four groups are coplanar with the aromatic ring. The Na⁺ cation has a distorted octahedral coordination made up of two cis-coordinated water mol­ecules and the O atoms of four carboxyl groups belonging to four different dianions; the water mol­ecule acts as a bridge between two Na⁺ ions related by an inversion center.