Polymorphism of the Ag8S4O4 and Ag6S3O4 compounds

Experimental results of the reaction occurring between aqueous solutions of AgNO3 and Na2S2O3 were presented in this work. It has been demonstrated that these reagents form two phases to which the summary formulas: alpha-Ag8S4O4 and alpha-Ag6S3O4 were ascribed. The alpha-Ag8S4O4 phase crystallizes in a tetragonal system and has the following parameters of the unit cell: a = b = 0.72052 nm, c = 0.51140 nm, V = 0.26550 nm(3), Z = 1, d(x) = 6.60 g/cm(3). At 223 degrees C alpha-Ag8S4O4 undergoes an irreversible, endothermic polymorphic transition. The heat of this transition amounts 8.03 x 10(-3) J/mol. A high-temperature polymorphic form beta-Ag8S4O4 melts at 400 degrees C. The alpha-Ag6S3O4 phase crystallizes in a monoclinic system and has the following parameters of the unit cell: a = 2.09616 nm, b = 0.53118 nm, c = 1.49885 nm, beta = 102.78 degrees, V = 1.62753 nm(3), Z = 8, d(x) = 6.59 g/cm(3). alpha-Ag6S3O4 also undergoes an irreversible, endothermic polymorphic transition at 221 degrees C. The heat of this transition amounts 7.65 x 10(-3) J/mol. A high-temperature form, beta-Ag6S3O4, melts at 390 degrees C. (C) 2000 Kluwer Academic Publishers.