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: -Ag₈S₄O₄ and -Ag₆S₃O₄ were ascribed. The -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 nm³, Z = 1, d_x = 6.60 g/cm³. At 223°C -Ag₈S₄O₄ undergoes an irreversible, endothermic polymorphic transition. The heat of this transition amounts 8.03 × 10^–3 J/mol. A high-temperature polymorphic form -Ag₈S₄O₄ melts at 400°C. The -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, = 102.78°, V = 1.62753 nm³, Z = 8, d_x = 6.59 g/cm³. -Ag₆S₃O₄ also undergoes an irreversible, endothermic polymorphic transition at 221°C. The heat of this transition amounts 7.65 × 10^–3 J/mol. A high-temperature form, -Ag₆S₃O₄, melts at 390°C.