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

The title compound, C(8)H(4)Br(3)NO(4), 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.