1-Carboxy­methyl-3-iodo-1-pyridinium–iodide–(3-iodo-1-pyridinio)­acetate (1/1/1)

The title compound, C₇H₇I₂NO₂⁺·I⁻·C₇H₆I₂NO₂, crystallizes with Z′ = ; the iodide anion lies on a twofold axis, and in the cation/zwitterion adduct the acidic H atom is disordered over an inversion centre. The residues are linked to form zigzag chains in the overall direction [103] by I...I interactions between anion and cation, and by classical O—H...O hydrogen bonds. Weak hydrogen bonds C—H...O link the chains to form layers parallel to (30).