THE CRYSTAL AND MOLECULAR-STRUCTURE OF THE AMMONIUM BISMUTH CITRATE DIHYDRATE [(NH4)+BI(C6H4O7)-].2H2O

The crystal and molecular structure of ammonium citrate dihydrate [(NH4)+Bi(C6H4O7)-].2H2O has been established by means of X-ray diffraction on a single crystal using CuK-alpha-radiation. The crystals are monoclinic, space group C2/c with a = 1680.5(2), b = 1254.4(3), c = 1040.1(2) pm, beta = 91.27(2)-degrees, Z = 8. The structure was solved by the Patterson method, and was refined by least-squares techniques yielding final R(R(w)) values of 0.042 (0.034) based upon 1855 reflections. The citrate acts as a chelating and as a bridging ligand, thus forming a three-dimensional network with carboxy groups coordinating to bismuth in a mono- as well as a bidentate manner. The essential structural characteristics is the anion [(Bi-O-C6H4O6)-] that strikingly contains a four-basic citrate the hydroxy oxygen atom of which is covalently bonded to bismuth. Two water molecules and the ammonium ion are located in channels parallel to the z-axis.