The hydrated and anhydrous gold(III) tetrachloride salts of l‐ecgonine,an important forensic toxicology marker for cocaine

The structure of the hydrated gold(III) tetrachloride salt of l ‐ecgonine {hydronium tetrakis(1R,2R,3S,5S,8S)‐3‐hydroxy‐8‐methyl‐8‐azoniabicyclo3.2.1]octane‐2‐carboxylate pentakistetrachloridoaurate(III)] hexahydrate}, (C₉H₁₆NO₃)₄(H₃O)AuCl₄]₅·6H₂O, demonstrates an unprecedented stoichiometric relationship between the cations and anions in the unit cell. The previous tropane alkaloid structures, including the related hydrochloride salts, all have a cation–anion ratio of 1:1, as does the anhydrous salt described here, namely (1R,2R,3S,5S,8S)‐3‐hydroxy‐8‐methyl‐8‐azoniabicyclo3.2.1]octane‐2‐carboxylate tetrachloridoaurate(III), (C₉H₁₆NO₃)AuCl₄]. The hydrated salt, however, consists of four monopositive N‐protonated units of the alkaloid and five AuCl₄]^? counter‐ions, plus seven solvent water molecules. The H atom required for change balance has been assigned to a water molecule. In addition, the hydrate has a novel arrangement, with all seven of the water molecules and all of the O atoms in the cations participating in an alternating arrangement of interleaved sheets of the anionic species. Both the hydrate and the anhydrous salt of the same toxicologically important marker for cocaine show that the cation and anion are in close proximity to each other, as was found in the gold(III) tetrachloride salt of l ‐cocaine.