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} , 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(O_carbox)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).