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

Abstract

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.

Keywords:

• Sulfate
• thermal decomposition
• phase transition
• DSC
• evolved gas analysis
• diamminesilver(I)

Acknowledgements

The research within project No. VEKOP-2.3.2-16-2017-00013 was supported by the European Union and the State of Hungary, and co-financed by the European Regional Development Fund. Research in the Wigner RCP has been funded by the Hungarian National Research Fund (OTKA) Grant No. SNN 118012, and research equipment and infrastructure was provided by the Hungarian Academy of Sciences. B. Barta Holló acknowledges financial support of the Ministry of Education, Science and Technological Development of the Republic of Serbia (Grant No. 451-03-68/2020-14/200125). The research reported in this paper was also supported by the NRDI K 124212 and an NRDI TNN_16 123631 as well as the BME Nanotechnology and Materials Science TKP2020 IE grant of NKFIH Hungary (BME IE-NAT TKP2020). This work was supported by the National Research, Development and Innovation Office-NKFIH through OTKA grants KH129588 and K124544. High-temperature single crystal diffraction study on 1-HT was funded by the ELTE Thematic Excellence Programme supported by the Hungarian Ministry for Innovation and Technology. [SzintPlusz_1117]; and, as part of research within project No. VEKOP-2.3.3-15-2017-00018, it was supported by the European Union and the State of Hungary, and co-financed by the European Regional Development Fund.

Disclosure statement

No potential conflict of interest was reported by the authors.