Bis(dimethyl-ammonium) 3,3'-dicarb-oxy-5,5'-(5,7,12,14-tetra-oxo-6,13-diaza-tetra-cyclo-[6.6.2.0(4,16).0(11,15)]hexa-deca-1,3,8,10,15-penta-ene-6,13-di-yl)dibenzoate dihydrate.

The title compound, 2C(2)H(8)N(+)·C(30)H(12)N(2)O(12) (2-)·2H(2)O, comprises dimethyl-ammonium cations, 3,3'-dicarb-oxy-5,5'-(5,7,12,14-tetra-oxo-6,13-diaza-tetra-cyclo-[6.6.2.0(4,16).0(11,15)]hexa-deca-1,3,8,10,15-penta-ene-6,13-di-yl)dibenzoate dianions and water mol-ecules. The dianion is situated on a crystallographic inversion centre. Two very strong symmetry-restricted O⋯H⋯O hydrogen bonds are present which are situated about the crystallographic inversion centres. In one of these hydrogen bonds, the H atom is situated at its centre, while in the other one the H atom is disordered about its centre. Both H atoms are involved in the chain-like C(2) (2)(16) motif, and not in a more common motif R(2) (2)(8) that is composed of a pair of hydrogen carboxyl-ates with the H atoms situated about the centre between the pair of O atoms. In the crystal, inter-action of these hydrogen bonds results in formation of anionic layers of dianions parallel to (-111). The water mol-ecules donate their H atoms to one of two of the carboxyl-ate O atoms, forming strong hydrogen bonds. The dimethyl-ammonium donates a bifurcated hydrogen bond to an oxo group of the dianion, forming weak hydrogen bonds. All the hydrogen bonds form a three-dimensional hydrogen-bonded network.