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

The crystal structure is reported of sodium 2-[2-(2,6-di-chloro-anilino)phen-yl]acetate 3.5-hydrate or tetra-μ-aqua-κ8 O:O-deca-aqua-bis-{μ3-2-[2-(2,6-di-chloro-anilino)phen-yl]acetato-κ3 O:O:O}tetra-sodium(I) bis-{2-[2-(2,6-di-chloro-anil-ino)phen-yl]acetate}, {[Na4(C14H10Cl2NO2)2(H2O)14](C14H10Cl2NO2)2} n , which re-presents 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 carboxyl-ate 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-H⋯O hydrogen bonds stabilizes the crystal structure. The herein reported crystal structure for SD·3.5H2O in space group P is different from those previously reported for other hydrates, namely SD·4.75H2O (P21) and SD·5H2O (P21/m).