Dynamic disorder in the high-temperature polymorph of bis[diamminesilver(I)] sulfate—reasons and consequences of simultaneous ammonia release from two different polymorphs.

We prepared and characterized a high-t tetragonal polymorph of diamminesilver(I) sulfate (a = 8.6004(4) Å, c = 6.2123(6) Å) (compound 1-HT). The phase transformation of the low-temperature polymorph of diamminesilver(I) sulfate (compound 1-LT) into the high-temperature polymorph (compound 1-HT) partly coincides with the initial stage of the thermal decomposition of 1-LT. Selecting appropriate conditions, we separated the two processes and determined the standard heat of formation of the LT polymorph (ΔH²⁹⁸ = −1208.92 kJ/mol) and the enthalpy of polymorphic transformation (ΔH_LT→HT = 13.18 kJ/mol). The high-temperature XRD results showed that the lattice constants of the LT polymorph (1-LT) extend in the direction of a, b, and compress in the direction of c in the 1-HT polymorph. According to high temperature SXRD data, the Ag–Ag distance (in the direction of c) shortens from 3.20 Å (1-LT) to 3.11 Å (1-HT), while the extension in the a,b direction weakens/disrupts the N-H...O-S hydrogen bonds and the coordinative Ag...O-S interactions. The IR and Raman spectroscopic data confirm the weakening/breaking of N-H...O-S hydrogen bonds. A vacuum-assisted thermal deammoniation experiment of 1-LT in the preparation of monoamminesilver(I) sulfate showed that the product is the mixture of silver(I) sulfate and the initial diamminesilver(I) sulfate complex. [ABSTRACT FROM AUTHOR]