Structural and spin-glass properties of single crystal JeffJ_{eff} = 1/2 pyrochlore antiferromagnet NaCdCo2_2F7_7 : correlating TfT_f with magnetic-bond-disorder

Weak bond disorder disrupts the expected spin-liquid ground-state of the ideal $S$ = 1/2 Heisenberg pyrochlore antiferromagnet. Here we introduce a single crystal study of the structural and magnetic properties of the bond-disordered pyrochlore NaCdCo$_2$F$_7$. The magnetic susceptibility appears isotropic, with a large negative Curie-Weiss temperature ($\theta_{CW}$ = -108(1) K), however no magnetic order is observed on cooling until a spin-glass transition at $T_f$ = 4.0 K. AC-susceptibility measurements show a frequency-dependent shift of the associated cusp in $\chi$ at $T_f$, that can be fitted well by the empirical Vogel-Fulcher law. The magnetic moment of $\mu_{eff}$ = 5.4(1) $\mu_{B}$/Co$^{2+}$ indicates a significant orbital contribution and heat capacity measurements show that down to 1.8 K, well below $T_f$, only $S_{mag}$ ~2/3 Rln(2) of the magnetic entropy is recovered, suggestive of residual continued dynamics. Structural and magnetism comparisons are made with the other known members of the Na$A$Co$_2$F$_7$ family ($A$ = Ca$^{2+}$, Sr$^{2+}$), confirming the expected relationship between spin-glass freezing temperature, and extent of magnetic bond disorder brought about by the size mismatch between A-site ions

Crystal structure of 4-bromo-3-nitro-1H-pyrazole-5-carboxylic acid monohydrate, C4H2N3BrO4·H2O

C4H2N3BrO4·H2O, monoclinic, P21/c (no. 14), a = 7.177(2) Å, b = 10.999(3) Å, c = 10.414(3) Å, β = 100.145 (11) °, V = 809.3(4) Å3, Z = 4, Rgt (F) = 0.0379, wRref (F2) = 0.0714, T = 200K © 2023 the author(s), published by De Gruyter, Berlin/Boston

Intermediate valence behavior in CeCo9Si4

The novel ternary compound CeCo$_9$Si$_4$ has been studied by means of specific heat, magnetisation, and transport measurements. Single crystal X-ray Rietveld refinements reveal a fully ordered distribution of Ce, Co and Si atoms with the tetragonal space group I4/mcm isostructural with other RCo9Si4. The smaller lattice constants of CeCo9Si4 in comparison with the trend established by other RCo9Si4 is indicative for intermediate valence of cerium. While RCo9Si4 with R= Pr, .. Tb, and Y show ferromagnetism and LaCo9Si4 is nearly ferromagnetic, CeCo9Si4 remains paramagnetic even in external fields as large as 40 T, though its electronic specific heat coefficient (g~190 mJ/molK^2) is of similar magnitude as that of metamagnetic LaCo9Si4 and weakly ferromagnetic YCo9Si4.Comment: 2 pages, 3 figures, submitted to SCES 0

Superconductivity in novel Ge-based skutterudites: {Sr,Ba}Pt_4Ge_{12}

Combining experiments and ab initio models we report on $\rm SrPt_4Ge_{12}$ and $\rm BaPt_4Ge_{12}$ as members of a novel class of superconducting skutterudites, where Sr or Ba atoms stabilize a framework entirely formed by Ge-atoms. Below $T_c=5.35$ K, and 5.10 K for $\rm BaPt_4Ge_{12}$ and $\rm SrPt_4Ge_{12}$, respectively, electron-phonon coupled superconductivity emerges, ascribed to intrinsic features of the Pt-Ge framework, where Ge-$p$ states dominate the electronic structure at the Fermi energy.Comment: 4 pages, 4 figures, accepted for publication in PR

Sr-bearing high-pressure tourmaline from the Kreuzeck Mountains, Eastern Alps, Austria

A detailed investigation was conducted on high-pressure (~1.4 GPa) tourmaline from an Eoalpine mafic eclogite, which occurs in the Kreuzeck Mountains, Eastern Alps, Austria. Tourmaline from this locality contains the highest amount of Sr²⁺ (up to 0.68 wt% SrO) known to date. The space group is R3m with unit-cell parameters a = 15.944(1), c = 7.202(1) Å, V = 1585.5(3) ų. Analyses by a combination of electron microprobe, optical absorption spectroscopy and crystal-structure refinement (R1 = 1.31%) result in the structural formula ^X(Na_(0.85)Ca_(0.08)Sr_(0.06)K_(0.01))_(Σ1.00)^Y(Mg_(1.68)Al_(0.70) Fe_(0.37)³⁺Ti_(0.10)⁴⁺Fe_(0.11)²⁺Ca_(0.03)Cr_(0.01)³⁺)_(Σ3.00)^Z (Al_(5.15)Mg_(0.80)Fe_(0.05)³⁺)_(Σ6.00)^T(Si_(5.82)B_(0.10)Al_(0.08)O_(18)) (BO₃)₃^V(OH)₃^W [O_(0.45)(OH)_(0.35)F_(0.20)]. The T site contains mainly Si and additionally small amounts of B and Al. According to optical absorption spectroscopy (using the band near 1120 nm), the Fe³⁺/Fe ratio is 79 ± 2%, suggesting that this high-pressure tourmaline crystallized under oxidizing conditions. It has a significant oxy-dravite component. A near-rim zone contains 0.6 wt% Cr₂O₃, 0.5 wt% PbO₂, 0.2 wt% NiO and 0.1 wt% V₂O₃. Only a small F content was found by structure refinement. There is no evidence for significant X-site vacancy in the investigated tourmaline zones. We assume that the original boron source for tourmaline crystallization in the eclogite, i.e. tourmaline-bearing pegmatites in the country-rock, were influenced by a Sr-bearing marble

Crystal structure of 4-bromo-2-(1H-pyrazol-3-yl)phenol, C9H7BrN2O (vol 232, pg 507, 2017)

C9H7BrN2O, monoclinic, C2/c (no. 15), a = 16.255(3) angstrom, b = 4.4119(9) angstrom, c = 25.923(5) angstrom, beta = 107.99(3)degrees, V = 1768.2(7) angstrom(3), Z = 8, R-gt(F) = 0.0450, wR(ref)(F-2) = 0.0960, T = 150 K

Preparation, thermal analysis and spectral characterization of the 1 : 1 complexes of mercury(II) halides and Pseudohalides with 3,4,5,6-Tetrahydropyrimidine-2-thione. Crystal structures of bis(3,4,5,6-tetrahydropyrimidine-2-thione-S)mercury(II) tetrachloro and tetrabromomercurate(II)

Mercury(II) complexes of the type HgX2(H(4)pymtH) (X Cl- Br I-, SCN-, CN-; H(4)pymtH = 3,4,5, 6-tetrahydropyrimidine-2-thione) have been obtained and structurally characterized by X-ray diffraction, IR, H-1 and C-13 NMR spectroscopy. Single crystal X-ray structure analysis was performed for the chloro and bromo complexes, which were found to be isostructural. Their crystal structures consist of [Hg(H(4)pymtH)(2)](2+) complex cations and [HgX4](2-) complex anions interconnected by Hg . . .X contacts into puckered sheets. The crystal structure of H(4)pymtH has been redetermined to greater accuracy. In solution NMR spectra of complexes, the greatest complexation effects were found on the C-13 chemical shift of the thioketo-carbon atom and on the H-1 chemical shift of the NH protons

Preparation, Thermal Analysis and Spectral Characterization of the 1:1 Complexes of Mercury(II) Halides and Pseudohalides with 3,4,5,6-Tetrahydropyrimidine-2-thione. Crystal Structures of Bis(3,4,5,6-tetrahydropyrimidine-2-thione-S)mercury(II) Tetrachloro and Tetrabromomercurate(II)

Mercury(II) complexes of the type HgX2(H4pymtH) (X = Cl-, Br-, I-, SCN-, CN-; H4pymtH = 3,4,5,6-tetrahydropyrimidine-2-thione) have been obtained and structurally characterized by X-ray diffraction, IR, 1H and 13C NMR spectroscopy. Single crystal X-ray structure analysis was performed for the chloro and bromo complexes, which were found to be isostructural. Their crystal structures consist of [Hg(H4pymtH)2]2+ complex cations and [HgX4]2- complex anions interconnected by Hg⋅⋅⋅X contacts into puckered sheets. The crystal structure of H4pymtH has been redetermined to greater accuracy. In solution NMR spectra of complexes, the greatest complexation effects were found on the 13C Chemical shift of the thio-keto-carbon atom and on the 1H Chemical shift of the NH protons

Disodium tricopper(II) tetra­kis[selenate(IV)] tetra­hydrate

The title compound, Na2Cu3(SeO3)4(H2O)4, has been prepared under hydro­thermal conditions. The crystal structure contains a three-dimensional anionic framework made up from distorted [CuO4(H2O)2] octa­hedra ( symmetry), [CuO4(H2O)] square pyramids and trigonal-pyramidal SeO3 units sharing common corners. The connectivity among these units leads to four- and eight-membered polyhedral rings, which by edge-sharing inter­connect into walls. A rhombus-like 16-membered polyhedral ring channel system with a longest length of approximately 14.0 Å and a shortest length of 5.3 Å is enclosed by such walls along the a axis. The water mol­ecules attached to the Cu atoms, as well as the electron lone pairs of the SeIV atoms, protrude into these channels. The seven-coordinated Na+ counter-cations occupy the remaining free space of the 16-membered polyhedral ring channels. An intricate network of O—H⋯O hydrogen bonds further consolidates the three-dimensional structure