Crystal structure of a new hydrate form of the NSAID sodium diclofenac

.The crystal structure is reported of sodium 2-[2-(2,6-dichloroanilino)phenyl]- acetate 3.5-hydrate or tetra--aqua-8 O:O-decaaquabis{3-2-[2-(2,6-dichloroanilino)phenyl]acetato-3 O:O:O}tetrasodium(I) bis{2-[2-(2,6-dichloroanilino)- phenyl]acetate}, {[Na4(C14H10Cl2NO2)2(H2O)14](C14H10Cl2NO2)2}n, which represents a new hydrate form of the NSAID sodium diclofenac (SD). The triclinic unit cell contains one ionic compound with formula Na4(C14H10Cl2NO2)4(H2O)14, in which two symmetry-related carboxylate anions C14H10Cl2NO2 are bonded to a centrosymmetric [Na4] 4+ core cationic cluster, while the others are only hydrogen bonded to the cationic cluster. The conformation for the anions is similar to that found in other diclofenac compounds, and the [Na4(Ocarbox)2(H2O)14] 4+ cluster displays an unprecedented geometry, which can be described as an incomplete dicubane cluster formed by face-sharing incomplete cubes. A complex framework of O—HO hydrogen bonds stabilizes the crystal structure. The herein reported crystal structure for SD3.5H2O in space group P1 is different from those previously reported for other hydrates, namely SD4.75H2O (P21) and SD5H2O (P21/m).