5-Amino-2,4,6-tribromoisophthalic acid: the MAD triangle for experimental phasing

The title compound, C8H4Br3NO4, shows an extensive hydrogen-bond network. In the crystal structure, mol­ecules are linked into chains by COO—H⋯O bonds, and pairs of chains are connected by additional COO—H⋯O bonds. This chain bundle shows stacking inter­actions and weak N—H⋯O hydrogen bonds with adjacent chain bundles. The three Br atoms present in the mol­ecule form an equilateral triangle. This can be easily identified in the heavy-atom substructure when this compound is used as a heavy-atom derivative for experimental phasing of macromolecules. The title compound crystallizes as a nonmerohedral twin.