Mariana Derzsi, Armand Budzianowski, Viktor V. Struzhkin, Przemysław J. Malinowski, Piotr J. Leszczyński, Zoran Mazejd and Wojciech Grochala
Dominik Kurzydłowski, Marianna Derzsi, Armand Budzianowski, Zvonko Jagličić, Wiktor Koźmiński, Zoran Mazej, Wojciech Grochala
Dediacted to the memory of Neil Bartlett
We report the crystal structure and magnetic properties of a novel β polymorph of K2AgF4. β-K2AgF4 is paramagnetic above 20 K and exhibits a low Curie temperature (θ < 5 K). Solid state DFT (GGA and GGA+U) calculations were performed to analyze the electronic and magnetic structure of β-K2AgF4 at 0 K/0 GPa, reproducing correctly the ferromagnetic (FM) semiconductor ground state with the band gap at the Fermi level of approximately 1.65eV. Furthermore, we show that the novel β form is thermodynamically favoured over the previously reported two-dimensional α form and can be formed either by slow spontaneous exothermic α to β phase transition occurring on heating or direct synthesis from KF and AgF2 at 300°C. The relative stability of the α and β phases is rationalized in terms of the size of the M+cation in the M2M′F4 series (M = Na, K, Cs, M′ = Cu, Ag) and the mismatch between [MF] and [M′F4/2] sublattices in the layered perovskite α form.
Tomasz Michałowski, Zoran Mazej, Armand Budzianowski, Zvonko Jagličić, Piotr J. Leszczyński, and Wojciech Grochala
Wojciech Grochala, Michał Ksawery Cyrański, Mariana Derzsi, Tomasz Michałowski, Przemysław J. Malinowski, Zoran Mazej, Dominik Kurzydłowski, Wiktor Koźmiński, Armand Budzianowski and Piotr J. Leszczyński
Trifluoromethansulfonate of silver(I), AgSO3CF3 (abbreviated AgOTf), extensively used in organic chemistry, and its fluorosulfate homologue, AgSO3F, have been structurally characterized for the first time. The crystal structures of both homologues differ substantially from each other. AgOTf crystallizes in a hexagonal system (R space group, No.148) with a=b=5.312(3)Å and c=32.66(2)Å, while AgSO3F crystallizes in a monoclinic system in the centrosymmetric P21/m space group (No.11) with a=5.4128(10)Å, b=8.1739(14)Å, c=7.5436(17)Å, and β=94.599(18)°, adopting a unique structure type (100K data). There are two types of fluorosulfate anions in the structure; in one type the F atom is engaged in chemical bonding to Ag(I) and in the other type the F atom is terminal; accordingly, two resonances are seen in the 19F NMR spectrum of AgSO3F. Theoretical analysis of the electronic band structure and electronic density of states, as well as assignment of the mid- and far-infrared absorption and Raman scattering spectra for both compounds, have been performed based on the periodic DFT calculations. AgSO3F exhibits an unusually low melting temperature of 156°C and anomalously low value of melting heat (ca. 1 kJ mol−1), which we associate with (i) disorder of its anionic sublattice and (ii) the presence of 2D sheets in the crystal structure, which are weakly bonded with each othervia long Ag–O(F) contacts. AgSO3F decomposes thermally above 250°C, yielding mostly Ag2SO4 and liberating SO2F2. AgOTf is much more thermally stable than AgSO3F; it undergoes two consecutive crystallographic phase transitions at 284°C and 326°C followed by melting at 383°C; its thermal decomposition commences above 400°C leading at 500°C to crystalline Ag2SO4 and an unidentified phase as major products of decomposition in the solid state.
Przemysław Jan Malinowski, Mariana Derzsi, Armand Budzianowski, Piotr J. Leszczyński, Bartłomiej Gaweł, Zoran Mazej and Wojciech Grochala
O2 at low expense from AgIISO4: Silver(II) sulfate provides the first example among metal sulfates of low-temperature “reductive” thermal decomposition, which results in AgI disulfate and molecular dioxygen. Despite the similarity of this reaction to the one known for peroxodisulfates (e.g., K2S2O8), the thermodynamics and kinetics of both processes are markedly different, and when compared they severely disobey Hammond’s rule (see scheme).