Synthesis and characterization of the mixed valence Cu(l)/Cu(ll) 3,5-bis(trifluoromethyl)-pyrazolate complex, [Cu(ll)2Cu(l)(F6dmpz)5]

1997 ◽  
Vol 75 (5) ◽  
pp. 491-498 ◽  
Author(s):  
Martin K. Ehlert ◽  
Alan Storr ◽  
David A. Summers ◽  
Robert C. Thompson
Keyword(s):  
Exchange Coupling ◽  
Mixed Valence ◽  
Direct Methods ◽  
Magnetic Data ◽  
Antiferromagnetic Exchange ◽  
Coupling Constant ◽  
Copper Metal ◽  
X Ray ◽  
R Value

The reaction of molten 3,5-bis(trifluoromethyl)pyrazole (F6dmpzH) with copper metal shot under an atmosphere of dioxygen yields the green trimetallic mixed valence [Cu(II)2Cu(1)(F6dmpz)5]. Crystals of [Cu(II)2Cu(I)(F6dmpz)5] are triclinic, a = 9.0557(2), b = 9.6164(2), c = 11.8874(3) Å, α= 105.406(1)°, β = 112.317(1)°, γ = 90.662(1)°, Z= 1, space group P͞1. The crystal structure was solved by direct methods and was refined by full-matrix least-squares procedures to a final R value of 0.0538 for 2591 reflections with I≥2σ(I). Magnetic susceptibility studies over the range 2–300 K reveal strong antiferromagnetic exchange coupling between the two copper(II) centers. Fits of the magnetic data to the Bleaney-Bowers equation for two interacting S= ½ centers gives the exchange coupling constant J = –235 cm–1. Key words: trimetallic, copper, 3,5-bis(trifluoromethyl)pyrazolates, X-ray structure, antiferromagnetism.

Metal pyrazolate polymers. Part 1. Synthesis, structure, and magnetic properties of the [Cu(pz)2]x polymer

1989 ◽  
Vol 67 (11) ◽  
pp. 1970-1974 ◽  
Author(s):  
M. K. Ehlert ◽  
S. J. Rettig ◽  
A. Storr ◽  
R. C. Thompson ◽  
J. Trotter
Keyword(s):  
Crystal Structure ◽  
Direct Methods ◽  
Magnetic Data ◽  
Coordination Geometry ◽  
Antiferromagnetic Exchange ◽  
Chain Polymer ◽  
X Ray ◽  
Linear Chains ◽  
Polymeric Chains ◽  
Distorted Tetrahedral Coordination

A novel and reliable method for the synthesis of polybis(μ-pyrazolato-N,N′)copper(II), [Cu(pz)2]x(where pz = N2C3H3), is presented. Single crystals of the polymer suitable for X-ray study have been grown under carefully controlled conditions. Crystals of polybis(μ-pyrazolato-N,N′)copper(II) are orthorhombic, a = 7.917(1), b = 11.491(2), c = 7.778(1) Å, Z = 4, space group Ibam. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.029 and Rw = 0.038 for 507 reflections with I ≥ 3σ(I). The crystal structure consists of infinite double-bridged polymeric chains. The Cu atom has a D2 distorted tetrahedral coordination geometry with Cu—N = 1.957(2) Å and N—Cu—N = 94.3(1)–139.5(1)°. Magnetic susceptibility studies (4.2 to 299 K) on this material reveal very strong antiferromagnetic exchange between copper(II) centres in the extended linear chains. The magnetic data have been successfully analyzed according to the isotropic Heisenberg model for linear chains with −J = 78 cm−1 and g = 2.12. Keywords: crystal structure, copper(II) pyrazolate chain polymer, antiferromagnetic exchange.

Metal pyrazolate polymers. Part 2. Synthesis, structure, and magnetic properties of [Cu(4-Xpz)2]x polymers (where X = Cl, Br, Me, H; pz = pyrazolate)

1991 ◽  
Vol 69 (3) ◽  
pp. 432-439 ◽  
Author(s):  
Martin K. Ehlert ◽  
Steven J. Rettig ◽  
Alan Storr ◽  
Robert C. Thompson ◽  
James Trotter
Keyword(s):  
Exchange Coupling ◽  
Structural Parameters ◽  
Magnetic Data ◽  
Antiferromagnetic Exchange ◽  
Coupling Constant ◽  
Orthorhombic Space Group ◽  
Magnetic Exchange ◽  
Linear Chains ◽  
Green Form ◽  
Reliable Methods

Novel and reliable methods for the synthesis of the polymers [Cu(4-Xpz)2]x (where X = H, Cl, Br, and Me; pz = pyrazolate) are presented. The X = Cl compound was obtained as green and brown forms. Single crystals of the polymers with X = Me and X = Cl (green form) suitable for X-ray analysis have been obtained. [Cu(4-Mepz)2]x and [Cu(4-Clpz)2]x are isomorphous, crystallizing with four formula units per unit-cell in the orthorhombic space group Ibam, a = 9.7436(6), 9.155(4), b = 12.6106(8), 12.968(6), and c = 7.7482(6), 7.717(5) Å, respectively, for the 4-Me and 4-Cl derivatives. The structures were refined by full-matrix least-squares procedures to R = 0.027 and 0.041 for 430 and 246 reflections with I ≥ 3σ(I), respectively. Magnetic susceptibility studies over the temperature range 2 to 300 K have revealed that all the polymers exhibit very strong antiferromagnetic exchange between copper(II) centres in the extended linear chains. Discontinuities displayed in the susceptibility versus temperature plots suggest the presence of phase transitions at ~133 and ~108 K in the X = Cl (green form) and X = Br materials, respectively. The four compounds, X = H, Br, Me, and Cl (green form) also exhibit thermochromism over the 77 to 176 K region. The magnetic data have been analyzed employing an isotropic Heisenberg model for antiferromagnetic exchange in extended chain polymers. Values of the exchange coupling constant, J, for the room temperature forms of these materials are determined as −81, −105, −96, −104, and −88 cm−1 for 4-X = H, Br, Me, Cl (green form), and Cl (brown form), respectively. The magnitude of the exchange coupling is discussed in relation to structural parameters for the X = H, Me, and Cl (green form) compounds. Key words: copper(II) 4-substituted pyrazolate polymers, crystal structures, magnetic exchange.

Synthesis, Crystal Structure and Electrochemistry of μ-Acetatodi-μ-hydroxo-bis[(1,4,7-triazacyclononane)ruthenium(III)]-tris-iodide. Characterization of Some Ru(II)—Ru(III) Mixed Valence Species

1984 ◽  
Vol 39 (10) ◽  
pp. 1335-1343 ◽  
Author(s):  
Karl Wieghardt ◽  
Willy Herrmann ◽  
Martin Koppen ◽  
Ibrahim Jibril ◽  
Gottfried Hüttner
Keyword(s):  
Mixed Valence ◽  
Bond Distance ◽  
Direct Methods ◽  
Monoclinic Space Group ◽  
X Ray Diffraction ◽  
Reaction Conditions ◽  
X Ray ◽  
Mononuclear Complexes ◽  
Second Wave

A series of mononuclear complexes of ruthenium containing the cyclic triamine ligand 1,4,7-triazacyclononane ([9]aneN3 = L; C6H15N3) have been prepared: [RuIIL (dmso)2Cl]Cl (dmso = dimethyl sulfoxide), [RuIIILX3] (X = C1- , Br-), [RuL2](PF6)2, [RuL(C2O4)I]. Hydrolyses of RuLCl3 under a variety of reaction conditions afford dinuclear species:[RuIII2L2(μ-OH)2(μ-CH3CO2)]I3·H2O , [RuIII2L2(μ-OH)2Cl2](PF6)2, and the mixed-valence species [Ru2L2(μ-Cl)3](PF6)2. The complex [Ru2L2(μ-OH)2(μ-CH3CO2)]I3-H2O has been characterized by a single-crystal X-ray diffraction study. The compound crystallizes in the monoclinic space group P21/c with a = 14.70(1) Å , b = 19.00(1) Å , c = 9.714(7) Å , β = 99.62(7)°, and V = 2674 Å3, dcalcd = 2.37 g cm-3 for Z = 4, and mol wt 952.3. The structure was solved by direct methods using 2519 unique reflections with I > 2σ(I). Final residuals were R1 = 0.0615 and R2 = 0.075. The structure consists of μ-hydroxo- and μ-acetato- bridged dinuclear cations and iodide anions. The observed diamagnetism and a short Ru-Ru bond distance of 2.572(3) Å are indicative of a Ru-Ru single bond. The electrochemical properties of [Ru2L2(μ-OH)2(μ-CH3CO2)]3+ and [Ru2L2(μ-Cl)3]2+ have been investigated by cyclic voltammetry, and by coulometry. Two one-electron redox processes have been identified for both complexes the first of which exhibits a reversible wave, whereas the second wave at more negative potentials is irreversible. The blue mixed valence species [Ru2L2(μ-OH)2(μ-CH3CO2)]2+ has been characterized in solution.

scholarly journals PROXIMITY EFFECTS AND CURIE TEMPERATURE ENHANCEMENT IN Co/EuS AND Fe/EuS MULTILAYERS

SPIN ◽  
2012 ◽  
Vol 02 (04) ◽  
pp. 1250016 ◽  
Author(s):  
B. LEWITZ ◽  
A. STRAUB ◽  
V. KAPAKLIS ◽  
P. POULOPOULOS ◽  
A. DELIMITIS ◽  
...  
Keyword(s):  
Curie Temperature ◽  
Exchange Coupling ◽  
Proximity Effects ◽  
Antiferromagnetic Exchange ◽  
Coupling Constant ◽  
Polycrystalline Structure ◽  
Individual Layer ◽  
Temperature Enhancement ◽  
The Individual ◽  
Almost Continuous

Two identical Co/EuS and Fe/EuS multilayers of six periods each and with individual layers of about 4 nm thick are grown by e-beam evaporation under ultrahigh vacuum conditions. The films show polycrystalline structure with a grain size limited by the individual layer thickness. Both multilayers consist of almost continuous layers with some roughness. The surface peak-to-peak roughness is about 4–5 nm. Magnetization measurements and calculations of the loops based on a Stoner–Wohlfarth-like model allow us to determine the direct antiferromagnetic exchange coupling constant between the 3d metal and EuS at 5 K. Both samples show strong enhancement of the Curie temperature of EuS up to at least 50 K with a EuS magnetization tail, which persists up to about 100 K. The J = 7/2 character of the EuS layers is shown to be responsible for the large Curie temperature enhancement.

scholarly journals Coordination chemistry and photoswitching of dinuclear macrocyclic cadmium-, nickel-, and zinc complexes containing azobenzene carboxylato co-ligands

2019 ◽  
Vol 15 ◽  
pp. 840-851
Author(s):  
Jennifer Klose ◽  
Tobias Severin ◽  
Peter Hahn ◽  
Alexander Jeremies ◽  
Jens Bergmann ◽  
...  
Keyword(s):  
Exchange Coupling ◽  
Crystal Structure Analysis ◽  
Mixed Ligand ◽  
Ionization Mass ◽  
Coupling Constant ◽  
Magnetic Exchange ◽  
X Ray ◽  
Magnetic Exchange Coupling ◽  
Ferromagnetic Exchange ◽  
Single Crystal Structure Analysis

The synthesis of mixed-ligand complexes of the type [M2L(μ-L')]+, where L represents a 24-membered macrocyclic hexaaza-dithiophenolate ligand, L' is an azobenzene carboxylate co-ligand, and M = Cd(II), Ni(II) or Zn(II), is reported. A series of new complexes were synthesized, namely [M2L(μ-L')]+ (L' = azo-H, M = Cd (1), Ni (2); L' = azo-OH, M = Zn (3), Ni (4); L' = azo-NMe2, M = Zn (5), Cd (6), Ni (7); L' = azo-CO2Me, M = Cd (8), Ni (9)), and characterized by elemental analysis, electrospray ionization mass spectrometry (ESIMS), IR, UV–vis and NMR spectroscopy (for diamagnetic Zn and Cd complexes) and X-ray single crystal structure analysis. The crystal structures of 3' and 5–8 display an isostructural series of compounds with bridging azobenzene carboxylates in the trans form. The paramagnetic Ni complexes 2, 4 and 7 reveal a weak ferromagnetic exchange interaction with magnetic exchange coupling constant values between 21 and 23 cm−1 (H = −2JS1S2). Irradiation of 1 with λ = 365 nm reveals a photoisomerization of the co-ligand from the trans to the cis form.

Preparation, properties, and X-ray crystal structure of a 1:1 complex of tetrathiafulvalene and p-dinitrobenzene

1982 ◽  
Vol 60 (16) ◽  
pp. 2057-2061 ◽  
Author(s):  
Martin R. Bryce ◽  
Anthony S. Secco ◽  
James Trotter ◽  
Larry Weiler
Keyword(s):  
Crystal Structure ◽  
Room Temperature ◽  
Direct Methods ◽  
X Ray Diffraction ◽  
Crystalline Complex ◽  
X Ray ◽  
Triclinic System ◽  
Donor Acceptor ◽  
Bulk Magnetic Susceptibility ◽  
R Value

A crystalline complex of tetrathiafulvalene and p-dinitrobenzene has been prepared and characterised by esr and ir spectroscopy, bulk magnetic susceptibility, dc conductivity, and an X-ray diffraction analysis. It is a neutral 1:1 complex which is an insulator at room temperature, σRT = 2.5 × 10−7 ohm−7 cm−1. The complex crystallizes in the triclinic system, space group [Formula: see text] with cell constants a = 6.915(1), b = 7.615(1), c = 8.149(1) Å, α = 79.39(1), β = 69.55(1), γ = 70.81(1)°, Z = 1. Data were collected on an Enraf-Nonius CAD-4 diffractometer. The structure was solved by direct methods and refined to an R-value of 0.028 for 1222 observed reflections. The structure consists of molecules stacked in an alternating donor–acceptor fashion along the c-axis. Mixed sheets parallel to [Formula: see text] are comprised of tetrathiafulvalene and p-dinitrobenzene molecules arranged end-on in the [021] direction.

A Molecular Chain of Four CoII Ions Stabilized by a Tris-Pyridyl/Bis-?-Diketonate Ligand

2009 ◽  
Vol 62 (9) ◽  
pp. 1130 ◽  
Author(s):  
Leoní A. Barrios ◽  
David Aguilà ◽  
Olivier Roubeau ◽  
Keith S. Murray ◽  
Guillem Aromí
Keyword(s):  
Exchange Interactions ◽  
Molecular Chain ◽  
Water Molecules ◽  
Spin Orbit Coupling ◽  
Antiferromagnetic Exchange ◽  
X Ray Diffraction ◽  
X Ray ◽  
Bulk Magnetization ◽  
Hexadentate Ligand

The synthesis and characterization of a tris-pyridyl/bis-β-diketone molecule (H2L) is reported. This compound acts as a hexadentate ligand towards CoII to facilitate the assembly of a tetranuclear molecular chain of closely spaced metals with formula [Co4L2(MeOH)8](NO3)4 (1), which exhibits a very flat [Co4L2]4+ platform, as determined by single-crystal X-ray diffraction crystallography. Complex 1 readily exchanges axial methanol ligands with water molecules. The bulk magnetization of the resulting hydrate, 1a, shows that the metals in the [Co4L2]4+ moiety exhibit spin-orbit coupling and antiferromagnetic exchange interactions.

Structural and Magnetic Characterization of Rare Earth and Transition Metal Films Grown on Epitaxial Buffer Films on Semiconductor

1989 ◽  
Vol 151 ◽  
Author(s):  
R. F. C. Farrow ◽  
S. S. P. Parkin ◽  
V. S. Speriosu ◽  
A. Bezinge ◽  
A. P. Segmuller
Keyword(s):  
Rare Earth ◽  
Structural Characteristics ◽  
Metal Films ◽  
Epitaxial Films ◽  
Coherency Strain ◽  
Magnetic Data ◽  
Bulk Crystals ◽  
Structural Effects ◽  
X Ray

ABSTRACTStructural and magnetic data are presented and discussed for epitaxial films of rare earth metals ( Dy, Ho, Er) on LaF3 films on the GaAs(TTT) surface and Fe on Ag films on the GaAs(001) surface. Both systems exhibit unusual structural characteristics which influence the magnetic properties of the metal films. In the case of rare earth epitaxy on LaF3 we present evidence for epitaxy across an incommensurate or discommensurate interface. Coherency strain is not transmitted into the metal which behaves much like bulk crystals of the rare earths. In the case of Fe films , tilted epitaxy and long-range coherency strain are confirmed by X-ray diffractometry. Methods of controlling some of these structural effects by modifying the epitaxial structures are presented.

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