Pamoic acid determined from powder diffraction data

Abstract

The title compound [systematic name: 4,4′-methyl­enebis(3-hydr­oxy-2-naphthoic acid)], C23H16O6, has one half-mol­ecule in the asymmetric unit. The mol­ecular twofold rotational axis about the central C atom is preserved on crystallization. A chain formed by R22(8) hydrogen bonds runs along the c axis and an intra­molecular O—H⋯O=C—OH hydrogen bond is also formed. The crystal structure was solved by simulated annealing from laboratory X-ray powder diffraction data, with data collected at room temperature. Rietveld refinement of this model led to a final Rwp value of 0.0391 at 1.39 A resolution.