Browsing by Author "Conrad, Matthias"

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  • The Crystal Structure of MnF3 Revisited
    (2020-07-15) Bandemehr, Jascha; Stoll, Christiane; Heymann, Gunter; Ivlev, Sergei I.; Karttunen, Antti J.; Conrad, Matthias; Huppertz, Hubert; Kraus, Florian
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We correct the crystal structure of MnF 3, of which the space group was reported as monoclinic C2/c (no. 15) with a = 8.9202, b = 5.0472, c = 13.4748 Å, β = 92.64°, V = 606.02 ų, Z = 12, mS48, T not given, likely 298 K. In the structure model proposed here, we use a unit cell of one third of the former volume. The ruby red crystals of MnF 3 were synthesized by a high-pressure/high-temperature method, where MnF 4 was used as a starting material. As determined on a single crystal, MnF 3 crystallizes in the monoclinic space group I2/a (no. 15) with a = 5.4964(11), b = 5.0084(10), c = 7.2411(14) Å, β = 93.00(3)°, V = 199.06(7) Å 3, Z = 4, mS16, T = 183(2) K. The crystal structure of MnF 3 is related by a direct group-subgroup transition to the VF 3 structure-type. We performed quantum chemical calculations on the crystal structure to allow the assignment of bands of the obtained vibrational spectra.
  • The Crystal Structures of α- and β-F 2 Revisited
    (2019-01-01) Ivlev, Sergei I.; Karttunen, Antti J.; Hoelzel, Markus; Conrad, Matthias; Kraus, Florian
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The crystal structures of α-F 2 and β-F 2 have been reinvestigated using neutron powder diffraction. For the low-temperature phase α-F 2 , which is stable below circa 45.6 K, the monoclinic space group C2/c with lattice parameters a=5.4780(12), b=3.2701(7), c=7.2651(17) Å, β=102.088(18)°, V=127.26(5) Å 3 , mS8, Z=4 at 10 K can now be confirmed. The structure model was significantly improved, allowed for the anisotropic refinement of the F atom, and an F−F bond length of 1.404(12) Å was obtained, which is in excellent agreement with spectroscopic data and high-level quantum chemical predictions. The high-temperature phase β-F 2 , stable between circa 45.6 K and the melting point of 53.53 K, crystallizes in the cubic primitive space group Pm (Formula presented.) n with the lattice parameter a=6.5314(15) Å, V=278.62(11) Å 3 , cP16, Z=8, at 48 K. β-F 2 is isotypic to γ-O 2 and δ-N 2 . The centres of gravity of the F 2 molecules are arranged like the atoms in the Cr 3 Si structure type.
  • Crystal Structures of α- And β-Nitrogen Trifluoride
    (2019-05-06) Ivlev, Sergei I.; Conrad, Matthias; Hoelzel, Markus; Karttunen, Antti J.; Kraus, Florian
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The crystal structures of α-NF 3 and β-NF 3 are reported for the first time. As shown by powder neutron diffraction, the lowerature α-NF 3 crystallizes in the orthorhombic space group Pnma (oP16) with lattice parameters a = 6.71457(13) Å, b = 7.30913(14) Å, c = 4.55189(8) Å, V = 223.396(7) Å 3 , and Z = 4 at T = 6 K. The intramolecular atom distances in α-NF 3 are 1.3639(16) and 1.3677(11) Å for N-F, and 2.1216(16) and 2.120(2) Å for F···F. The F-N-F bond angles are 101.92(7)° and 101.63(10)°. All data are in excellent agreement with quantum-chemical predictions and previously reported experimentally obtained gas-phase data. The higherature β-NF 3 is a plastic crystal, space group P4 2 /mnm (tP120), with the lattice parameters a = 15.334(6) Å, c = 7.820(3) Å, V = 1838.6(12) Å 3 , and Z = 30 at T = 60 K. Its crystal structure is closely related to that of the Frank-Kasper sigma phase.
  • DFT-Guided Crystal Structure Redetermination and Lattice Dynamics of the Intermetallic Actinoid Compound UIr
    (2021-11-01) Sachs, Malte; Ivlev, Sergei I.; Etter, Martin; Conrad, Matthias; Karttunen, Antti J.; Kraus, Florian
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    UIr has been discussed as a rare example of a noncentrosymmetric, ferromagnetic superconductor crystallizing in the acentric PdBi structure type (P21, mP16). Here we present a new structure model for UIr. By means of single-crystal and powder X-ray diffraction we find UIr to crystallize in the centrosymmetric space group P21/c, in line with previous ab initio calculations. The discrepancy with the previous noncentrosymmetric model in space group P21 is explained by the occurrence of twinning. The observed twinning hints toward a high-temperature displacive phase transition of UIr to the CrB structure type (Cmcm, oS8): we discuss the lattice dynamics corresponding to this transition by crystallographic symmetry mode analysis and by density functional theory (DFT). We find that spin-orbit coupling is essential to understand this phase transition. We apply our theoretical considerations for a critical judgment of the structure models of UPt and NpIr that have been reported to crystallize isotypically with UIr. We confirm that UPt is isotypic to UIr (P21/c), whereas we predict NpIr to crystallize in the CrB structure type. Our report on the centrosymmetric crystal structure of UIr has an effect on all those theoretical models that investigated potentially novel superconducting coupling mechanisms of this compound on the basis of the noncentrosymmetric structure model.
  • The Fluoroperovskite TlMnF3
    (2018) Conrad, Matthias; Pietzonka, Clemens; Bernzen, Janek; Motta, Viviana; Weitzel, Karl Michael; Karttunen, Antti J.; Kraus, Florian
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    TlMnF3 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.
  • The Interhalogen Cations [Br2F5]+ and [Br3F8]+
    (2018-10-26) Ivlev, Sergei I.; Karttunen, Antti J.; Buchner, Magnus R.; Conrad, Matthias; Kraus, Florian
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The synthesis and characterization of unique polyhalogen cations containing μ-bridging fluorine atoms are reported. The [Br2F5]+ cation features a symmetric [F2Br-μ-F-BrF2] bridge, whereas the [Br3F8]+ contains asymmetric μ-F bridges. These fluoronium ions, obtained as [SbF6]- salts, were investigated using Raman and 19FNMR spectroscopy, as well as single-crystal X-ray diffraction. Quantum chemical calculations were carried out for the gas-phase cations as well as for the solid-state compounds. Population analyses show the μ-F atoms to possess the most negative partial charge within the cations.
  • Synthesis and characterization of barium hexafluoridoosmates
    (2018-01-01) Ivlev, Sergei I.; Karttunen, Antti J.; Buchner, Magnus R.; Conrad, Matthias; Ostvald, Roman V.; Kraus, Florian
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Two barium hexafluoridoosmates, Ba(OsF6)2 and BaOsF6, were synthesized and were characterized for the first time using X-ray powder and single crystal diffraction, IR spectroscopy, as well as NMR spectroscopy in anhydrous hydrogen fluoride. Ba(OsF6)2 crystallizes in the space group type P21/c with the cell parameters a = 6.4599(4), b = 10.7931(8), c = 14.7476(10) Å, β = 115.195(5)◦, V = 930.42(12) Å3, Z = 4 at 293 K. BaOsF6 crystallizes in the space group type R3 with the cell parameters a = 7.3286(10), c = 7.2658(15) Å, V = 337.95(12) Å3, Z = 3 at 100 K. Additionally, we have obtained the compounds Ba(OsF6)2·3BrF3, Ba(OsF6)2·HF, Ba(OsF6)2·6H2O from the respective solvents, and Ba(OsF6)2.
  • The [U2F12]2- Anion of Sr[U2F12]
    (2018-01) Scheibe, Benjamin; Pietzonka, Clemens; Mustonen, Otto; Karppinen, Maarit; Karttunen, Antti J.; Atanasov, Mihail; Neese, Frank; Conrad, Matthias; Kraus, Florian
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The 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.