MS16-P21 Synthesis and properties of puninite-type A2Cu3O(SO4)3 (A = Na, K, Rb, Cs) sulfate materials. Mineral puninite, Na2Cu3O(SO4)3 was described recently  in fumaroles of Tolbachik volcano.
Crystal structure of puninite is based on oxocentered [O2Cu6]8+ dimers. Four sulphate tetrahedra are ‘face-to-face’ attached to the dimers, whereas the other sulphate tetrahedral groups provide their linkage in two dimensions. Structural architecture of puninite can be described as being organized via a “host-guest” principle.
Five new compounds with the general formula A2Cu3O(SO4)3 (A = Na, K, Na/K, Rb, Cs) were obtained by solid-state reactions using anhydrous reagents A2SO4 (A = Na, K, Rb, Cs), CuSO4 and CuO mixed in the stoichiometric ratios. The reaction mixture was loaded into platinum crucibles, and kept at 600 °C for 3 h in air, followed by cooling to 25 °C at a cooling rate of 10 °C/min. The products consisted of green crystals of different shape. Pure powder sample of Na2Cu3O(SO4)3 was prepared for the investigation of magnetic properties, electrochemistry, IR spectroscopy and thermal behavior by the means of HT powder X-ray diffraction and DSC-TGA.
The Na2Cu3O(SO4)3 phase as a positive electrode was tested using Swagelok-type cells cycled at room temperature. The difficulties of electrochemical Na+ extraction have been encountered, and the removal of significant amount of sodium ions from the structure of the title compound was failed. Note, however, that our tests revealed an occurring of a probable redox process corresponding to the Cu2+/3+ transition at high voltage of around 4.8 vs Na+/Na.
This work was ﬁnancially supported by the Russian Science Foundation through the grant 16-17-10085. Ph.D. of D.O.N. is carried out within the framework of the international French–Russian co-tutorial Ph.D. program. D.O.N. also acknowledges support of the Saint-Petersburg State University through its internal grant. Technical support by the SPbSU X-ray Diffraction Resource Centre is gratefully acknowledged.
 Siidra O.I. et al. (2017) Copper oxosulphates from fumaroles of Tolbachik volcano: Puninite, Na2Cu3O(SO4)3 - a new mineral species and structure refinements of kamchatkite and alumoklyuchevskite, European Journal of Mineralogy, 29, 499-510.
Keywords: sulfate, X-ray diffraction