Dicalcium 1,4,5,8-naphthalenetetracarboxylate pentahydrate

In the title structure, the 1,4,5,8-naphthalenetetra-carboxylate anion possesses 2/m symmetry with the twofold axis coincident with the central C--C bond of the naphthalene rings. The ten atoms comprising the naphthalene core have a mean deviation of 0.033 A from the best least-squares plane describing these atoms, with the carboxyl C atom 0.395 (2) A removed from the plane. The dihedral angle between the carboxylate plane and the least-squares plane of the naphthalene rings is 46.2 (3) degrees. The O--C--O angle of the carboxylate group, 121.13(12) degrees, is smaller than normally expected, presumably due to the bidentate interaction with the Ca ion. The Ca ion is coordinated by eight O atoms: six carboxylate O atoms and two water O atoms. Because the Ca ion resides on a twofold axis there are only four independent Ca--O distances, which are in the range 2.368 (1)-2.681 (1)A. In this structure, the organic anions are separated by Ca ions and water molecules such that there are no short-range organic-organic interactions. One of the water molecules separating the organic anions is not involved in coordination with Ca, and is disordered.