55 research outputs found
Torque magnetometry study of magnetically ordered state and spin reorientation in the quasi-one-dimensional Heisenberg antiferromagnet CuSbO
We present an experimental study of macroscopic and microscopic magnetic
anisotropy of a spin tetramer system \cso using torque magnetometry and ESR
spectroscopy. Large rotation of macroscopic magnetic axes with temperature
observed from torque magnetometry agrees reasonably well with the rotation of
the tensor above ~K. Below 50~K, the
tensor is temperature independent, while macroscopic magnetic axes continue to
rotate. Additionally, the susceptibility anisotropy has a temperature
dependence which cannot be reconciled with the isotropic Heisenberg model of
interactions between spins. ESR linewidth analysis shows that anisotropic
exchange interaction must be present in \csos. These findings strongly support
the presence of anisotropic exchange interactions in the Hamiltonian of the
studied system. Below ~K, the system enters a long - range
antiferromagnetically ordered state with easy axis along the
direction. Small but significant rotation of magnetic axes is also observed in
the antiferromagnetically ordered state suggesting strong spin-lattice coupling
in this system.Comment: 10 pages, 10 figure
A Folded Conformation of 1,4,8,11-Tetrathiacyclotetradecane in its Mercury Compound: l,4,8,11-Tetrathiacyclotetradecanedipicratomercury( II) Heminitromethane, [Hg(C10H20S4)Ā· (C6H2N307)2] Ā· 1/2CH3N02
The crystals of 1,4,8,11-tetrathiacyclotetradecanedipicratomercury(
II) heminitromethane, [Hg(C10H20S4) Ā· (CsH2Ns01h] Ā· 1/2CHsN02,
are triclinic, spcrce group Pl with a = 1.2794(6), b = 1.3108(5), c =
= 1.0090(3) nm, a= 92.85(3) 0
, fJ = 107.67(3)0
, y = 94.54(4) 0
, V = 1.60236
nm3, and Z = 2. The structure was solved by the heavy atom
method and refined by the least-squares method to R = 0.030 for
the 7321 unique reflections. It consists of discrete, well separated
molecules. Coordination of the mercury atom is a distorted octahedron
with four sulfur atoms (Hg-S distances are 245.8(1),
251.9(1), 262 .. 9(2), and 305.0(2) pm) from the macrocycle and two
oxygen moms (Hg-0 distances are 253.1(3) and 255.8(3) pm) from
the two picrates. The macrocycle is folded so that three sulfur
atoms with short Hg-S bonds are in an equatorial and the fourth
in an apical position. The conformation of the coordinated macrocycle
is compared to the conformation of cyclotetradecane at 116 K
and to the conformation of the free crysta-lline macrocycle
Mechanochemical Synthesis of Alkaline Earth Mg ā Ba Saccharinates. Connectivity in the Crystal Structures of Mg(sac)2ā7H2O, Ca(sac)2ā7H2O and Ba(sac)2ā4.5H2O (sac = saccharinate)
Alkaline earth saccharinates Mg ā Ba were synthesized by the known solution-based methods and also by mechanochemical synthesis. The compounds were characterized by TG/DSC, X-ray powder diffraction, and Mg, Ca and Ba saccharinates by single-crystal X-ray analysis. The structure of Mg(sac)2ā7H2O (sac = saccharinate), is known but the diffraction data were collected at 170 K in this study for comparison with other structures. Crystals of hydrates of Ca ā Ba saccharinates are very thin needle-like. A 4 Ī¼m crystal of Ca(sac)2ā7H2O gave a low intensity diffraction pattern of sufficient quality to locate non-hydrogen atoms (triclinic crystal system, space group P-1, Z = 4). Crystals of strontium saccharinate were too thin for data collection, however the formula Sr(sac)2ā4H2O, proposed in a previous publication was confirmed by thermogravimetric analysis. Diffraction from a 12 Ī¼m thick crystal of Ba(sac)2ā4.5H2O resulted in a complete data set (monoclinic crystal system, space group P2/c, Z = 8). In the corresponding structures, the Mg ion is six-coordinated forming an octahedron, both Ca ions are irregularly eight-coordinated with the polyhedra bridged by saccharinate ions into chains, whereas both Ba ions are irregularly nine-coordinated with the polyhedra sharing edges and corners through bridging water molecules and bridging saccharinate ions into double chains. All water molecules are included into hydrogen bonding into layers with only van der Waals and weak CāHāāāO bonds between the chains
Effect of Hydrogen Bonding on the Pyramidalization of the Amino Group: Structure of 3,4-diaminobenzamidinium Chloride
3,4-diaminobenzamidinium was synthesized and spectroscopically and structurally characterized,
both at room temperature and at 150 K. The crystal structure consists of two 3,4-
diaminobenzamidinium cations and two chloride anions. The planar amidinium group is inclined by
35.35(5)Ā° and 28.96(7)Ā° in respect to the diaminobenzene moiety in the two crystallographically independent
cations. The ions are interconnected by a large network of hydrogen bonds into a threedimensional
structure. Pyramidalization of the amino group in relation to the hydrogen bond length in
which the amino group is an acceptor is analized. Two amino groups are acceptors of NāHĀ·Ā·Ā·N hydrogen
bonds of 2.9565(14) Ć
and 2.9654(15) Ć
resulting in pyramidalization of 340(1)Ā° and 337(1)Ā°, respectively
(the sum of the amino group bond angles is given as a measure of pyramidalization). A very weak
hydrogen bond to one amino group results in a very flat pyramid (351(1)Ā°), while one amino group is not
acceptor of a hydrogen bonds and it is planar. The resonance effect has influence on the planar amino
groups resulting in a shorter CāN(amino group) bond length than in the pyramidalized ones. (doi:
10.5562/cca2224
Mobility of Trace Elements in Pore Solutions of Portland Cement Pastes Exposed to Leaching
Two Portland cement pastes, CEM I 42.5R and CEM III/A 52.5N were exposed to leaching by soft water throughout a oneāyear hydration period. Mobility of trace elements was investigated by determination of their pore solution concentration in the course of time. Eleven trace elements were included in this research: antimony, arsenic, cadmium, chromium, cobalt, copper, mercury, nickel, lead, vanadium and zinc. The possible usage of the pore solution trace elements concentration in monitoring of deleterious leaching reactions and prediction of environmental risk was investigated.
This work is licensed under a Creative Commons Attribution 4.0 International License
Structure of the T6 Human Nickel Insulin Derivative at 1.35 Ć Resolution
This paper presents results of the structural investigation on the human insulin hexamer derivative stabilised by nickel coordination. Single crystals of the Ni-insulin derivative were prepared by the hanging drop vapour diffusion crystallisation method using metal-free insulin and nickel(II) acetate tetrahydrate. The low-temperature crystal structure was determined by the single crystal X-ray crystallographic method with data extending to 1.35 Ć
spacing. The investigated insulin derivative exhibits the T6 form of insulin and crystallizes in the trigonal system in space group R3, with the unit cell parameters a = b = 81.41 Ć
and c = 33.75 Ć
. There are two nickel atoms per insulin hexamer and both are octahedrally coordinated by three NĪµ2 atoms of three symmetry-related HisB10/HisD10 and three oxygen atoms of three symmetry-related water molecules
- ā¦