Crystal structures of the silver iodide sulfates Ag3ISO4 and Ag4I2SO4.

The crystal structures of two phases in the AgI-Ag2SO4 system, Ag3ISO4(AgI:Ag2SO4 = 1:1; systematic name: tris-ilver iodide sulfate), and Ag4I2SO4 (AgI:Ag2SO4 = 2:1; systematic name: tetra-silver diiodide sulfate), were determined by single-crystal X-ray diffraction. The crystal structure model of Ag3ISO4 contains triangularly arranged Ag atoms in zigzag ladder chains extending parallel to the a axis. The Ag zigzag ladder chains alternate with rows of SO4 groups, while iodine atoms are accommodated within the concavities of the zigzag ladders. The crystal structure of Ag4I2SO4 was refined using a split-atom model for two of the four Ag sites. The disordered Ag sites are situated between the layers containing SO4 groups parallel to the ac plane, whereas the Ag sites within the SO4 layers are fully occupied and exhibit no disorder. The positional disorder of some of the Ag sites is considered to be associated with the moderate ionic conductivity of Ag4I2SO4, approximately 10-3 S cm-1 at room temperature. This is the first report describing the crystal structures of compounds containing Ag+, SO4 2- and I-.