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-κ(8) O:O-deca-aqua-bis-{μ(3)-2-[2-(2,6-di-chloro-anilino)phen-yl]acetato-κ(3) O:O:O}tetra-sodium(I) bis-{2-[2-(2,6-di-chloro-anil-ino)phen-yl]acetate}, {[Na(4)(C(14)H(10)Cl(2)NO(2))(2)(H(2)O)(14)](C(14)H(10)Cl(2)NO(2))(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 Na(4)(C(14)H(10)Cl(2)NO(2))(4)(H(2)O)(14), in which two symmetry-related carboxyl-ate anions C(14)H(10)Cl(2)NO(2) (-) are bonded to a centrosymmetric [Na(4)](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 [Na(4)(O(carbox))(2)(H(2)O)(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·3.5H(2)O in space group P is different from those previously reported for other hydrates, namely SD·4.75H(2)O (P2(1)) and SD·5H(2)O (P2(1)/m).