Crystal stucture behaviour of a unique dodecanuclear cluster (NH4)12(Bi12O8cit8)(H2O)10

Colorless cubic crystals of a polymeric bismuth citrate may be synthesized by slow evaporation of an aqueous solution of bismuth citrate and ammonia. The polymer is a collection of dodecanuclear oxo-bismuth anionic units (Bi12O8cit4-8)12- bridged by carboxylate to citrates to form (NH4)12(Bi12O8cit8)(H2O)10. At higher concentrations, the solution is relatively homogeneous for Bi(12) aggregations, but at lower concentrations anionic clusters of Bi(12), Bi(24) and (Bi12)n are found. On adding citrate to the solution, a ligand exchange is observed resulting in dissociation of the clusters. The aqueous solution of the compound is compared to bismuth subcitrate, an ulcer healing agent.