Browsing by Author "Pietzonka, Clemens"
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- Coexistence of Two Different Distorted Octahedral [MnF6]3− Sites in K3[MnF6]: Manifestation in Spectroscopy and Magnetism
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-07-07) Stoll, Christiane; Atanasov, Mihail; Bandemehr, Jascha; Neese, Frank; Pietzonka, Clemens; Kraus, Florian; Karttunen, Antti J.; Seibald, Markus; Heymann, Gunter; Huppertz, HubertAs a consequence of the static Jahn-Teller effect of the 5E ground state of MnIII in cubic structures with octahedral parent geometries, their octahedral coordination spheres become distorted. In the case of six fluorido ligands, [MnF6]3− anions with two longer and four shorter Mn−F bonds making elongated octahedra are usually observed. Herein, we report the synthesis of the compound K3[MnF6] through a high-temperature approach and its crystallization by a high-pressure/high-temperature route. The main structural motifs are two quasi-isolated, octahedron-like [MnF6]3− anions of quite different nature compared to that met in ideal octahedral MnIII Jahn-Teller systems. Owing to the internal electric field of Ci symmetry dominated by the next-neighbour K+ ions acting on the MnIII sites, both sites, the pseudo-rhombic (site 1) and the pseudo-tetragonally elongated (site 2) [MnF6]3− anions are present in K3[MnF6]. The compound was characterized by single-crystal and powder X-ray diffraction, and magnetometry as well as by FTIR, Raman, and ligand field spectroscopy. A theoretical interpretation of the electronic structure and molecular geometry of the two Mn sites in the lattice is given by using a vibronic coupling model with parameters adjusted from multireference ab-initio cluster calculations. - The Fluoroperovskite TlMnF3
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2018) Conrad, Matthias; Pietzonka, Clemens; Bernzen, Janek; Motta, Viviana; Weitzel, Karl Michael; Karttunen, Antti J.; Kraus, FlorianTlMnF3 was obtained from the reduction of Tl3MnF6 under liquid ammonia, in which MnIII is obviously not redox-stable under the applied conditions. The crystal structure of TlMnF3 was determined on a single crystal using X-ray diffraction. The previously reported structure model was deduced from powder X-ray diffraction data only and therefore a much higher precision has been reached now. The compound crystallizes in the shape of colorless cubes with lattice parameters a = 4.2370(4) Å, V = 76.06(2) Å3 with Z = 1 at T = 140 K in the perovskite structure type (Pm3m, no. 221). At room temperature (T = 293 K), the lattice parameter of the slightly pink, almost colorless powderous compound is a = 4.2535(2) Å, V = 76.953(4) Å3. As the displacement parameter of the Tl atom was observed being rather large in comparison to the other atoms, the CAIT technique was used to demonstrate the mobility of the Tl cations. Additionally, quantum chemical calculations were carried out to further investigate the behavior of the Tl atoms. We calculate that most of the Tl atoms vibrate already at 75 K. Magnetic measurements showed that TlMnF3 is an antiferromagnet with TN = 82 K and a Weiss temperature θ of –151.2(2) K. - MoF5 revisited. A comprehensive study of MoF5
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2018-07-01) Stene, Riane E.; Scheibe, Benjamin; Pietzonka, Clemens; Karttunen, Antti J.; Petry, Winfried; Kraus, FlorianWhile the properties of molybdenum pentafluoride, MoF5, have been investigated in the past, there exists no comprehensive study of the compound. Additionally, many of these studies appear incoherent and offer contradictory explanations of some of the observed properties of MoF5. Consequently, a comprehensive examination of MoF5 is presented here, including a redetermination of the crystal structure of MoF5 using single crystal and powder X-ray diffraction, the reevaluation of its IR, Raman and UV–Vis spectrum, and a study of its density (3.50(2) g/cm3 @ 25 °C) and magnetic properties. Additionally, density functional theory (DFT) calculations were performed on the gas phase molecule Mo4F20 to provide a discussion of properties realized during investigation. Single crystal X-ray diffraction showed MoF5 to crystalize in the monoclinic, C2/m space group, as isolated tetramers having the formula Mo4F20. Magnetic measurements showed that when “MoF5” is cooled from the melt fast enough, paramagnetic species with S = ½ are present together with S = 0 species. These species may be described using the formula (MoF5)n (n = odd) and (MoF5)n (n = even, presumably n = 4). From the measurements, the content of the S = ½ species is estimated to be 6%. The preferred species of MoF5 under ambient conditions is Mo4F20. - NOUF6 Revisited
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2016-07-14) Scheibe, Benjamin; Lippert, Sina; Rudel, Stefan S.; Buchner, Magnus R.; Burghaus, Olaf; Pietzonka, Clemens; Koch, Martin; Karttunen, Antti J.; Kraus, FlorianWe have synthesized NOUF6 by direct reaction of NO with UF6 in anhydrous HF (aHF). Based on the unit cell volume and powder diffraction data, the compound was previously reported to be isotypic to O2PtF6, however, detailed structural data, such as the atom positions and all information that can be derived from those, were unavailable. We have therefore investigated the compound by using single-crystal and powder X-ray diffraction, IR, Raman, NMR, EPR, and photoluminescence spectroscopy, magnetic measurements, as well as chemical analysis, density determination, and quantum chemical calculations. - Syntheses and Characterization of the Mixed-Valent Manganese(II/III) Fluorides Mn2F5and Mn3F8
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-09-06) Bandemehr, Jascha; Zimmerhofer, Fabian; Ivlev, Sergei I.; Pietzonka, Clemens; Eklund, Kim; Karttunen, Antti J.; Huppertz, Hubert; Kraus, FlorianWe obtained single crystals of the binary mixed-valent fluorides Mn2F5 and Mn3F8 using a high-pressure/high-temperature approach. Mn2F5 crystallizes isotypic to CaCrF5 in the monoclinic space group C2/c (No. 15), with a = 8.7078(8) Å, b = 6.1473(6) Å, c = 7.7817(7) Å, β = 117.41(1)°, V = 369.80(6) Å3, Z = 4, and mC28 at T = 173 K. Mn3F8 crystallizes in the monoclinic space group P21 (No. 4) with a = 5.5253(2) Å, b = 4.8786(2) Å, c = 9.9124(4) Å, β = 92.608(2)°, V = 266.92(2) Å3, Z = 2, and mP22 at T = 183 K and presents a new structure type. Crystal-chemical reasoning, CHARDI calculations, and quantum-chemical calculations allowed for the assignment of the oxidation states of the Mn atoms. In both bulk compounds, MnF2 was present as an impurity, as evidenced by powder X-ray diffraction and IR and Raman spectroscopy. - Synthesis, Characterization, and Polymorphism of [H3O][NbF6]: A Polar and Possibly Ferroelectric Oxonium Salt
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2024-05-22) Möbs, Martin; Sachs, Malte; Rolheiser, Konstantin; Pietzonka, Clemens; Karttunen, Antti J.; Kraus, Florian[H3O][NbF6] was obtained from the controlled hydrolysis of NbF5 in anhydrous liquid HF. It adopts a polar, orthorhombic crystal structure with space group Iba2 (no. 45, oI88) at room temperature. A first-order phase transition at 137 K leads to a cubic non-centrosymmetric polymorph in space group I213 (no. 199, cI88). This low-temperature modification results from a distinct rotation of the [H3O]+ cations canceling their polar orientation in the room temperature phase. Quantum-chemical calculations estimate a rotational barrier between 5.8 to 6.4 kJ/mol. At a temperature of 363 K, the compound adopts a centrosymmetric, cubic crystal structure in space group Pm (Formula presented.) m (no. 221, cP11) that shows rotational disorder of cations and anions. The transition from the polar phase at room temperature to the centrosymmetric phase at high temperature not only reveals the plastic nature of the high-temperature structure but also hints at potential ferroelectric properties, underscoring the multifaceted behavior of [H3O][NbF6] across different temperature regimes. - The [U2F12]2- Anion of Sr[U2F12]
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2018-01) Scheibe, Benjamin; Pietzonka, Clemens; Mustonen, Otto; Karppinen, Maarit; Karttunen, Antti J.; Atanasov, Mihail; Neese, Frank; Conrad, Matthias; Kraus, FlorianThe D2h-symmetric dinuclear complex anion [U2F12]2- of pastel green Sr[U2F12] shows a hitherto unknown structural feature: The coordination polyhedra around the U atoms are edge-linked monocapped trigonal prisms, the UV atoms are therefore seven-coordinated. This leads to a U-U distance of 3.8913(6)Å. A weak UV-UV interaction is observed for the dinuclear [U2F12]2- complex and described by the antiferromagnetic exchange Jexp of circa -29.9cm-1. The crystalline compound can be easily prepared from SrF2 and β-UF5 in anhydrous hydrogen fluoride (aHF) at room temperature. It was studied by means of single crystal X-ray diffraction, IR, Raman and UV/VIS spectroscopy, magnetic measurements, and by molecular as well as by solid-state quantum chemical calculations.