CHARACTERIZATION OF PRECIPITATES FORMED FROM THE TETRAIODOMERCURATE RATE(II) ANION AND MERCURY(I) OR SILVER(I) CATIONS

The nature of precipitates formed from Hg-I or Ag-I and the complex an ion (HgI4)(2-) has been elucidated by means of X-ray diffraction (XRD) , scanning electron microscopy (SEM) and energy-dispersive X-ray micro analysis (EDX). In the case of Hg-I, well crystallized tetragonal Hg2I 2 is formed at the beginning of the precipitation from free I- ions. L ater, HgI2 precipitates in the form of filamentous masses. On the othe r hand, Ag-I gives rise first to the formation of hexagonal crystals o f AgI and, in a further stage, Ag-2(HgI4) also precipitates. On adding an excess of tetraiodomercurate(II) solution, AgI is dissolved while filamentous HgI2 precipitates. These results are rationalized, taking into account the various precipitation and complex formation equilibri a involved.