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 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.

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.

Interconnection of [V15As6O42(H2O)]6- Clusters by Cu2+-centered Complexes: Synthesis, Crystal Structure and Selected Properties

2014 ◽  
Vol 69 (11-12) ◽  
pp. 1306-1314 ◽  
Author(s):  
Adam Wutkowski ◽  
Christian Näther ◽  
Jan van Leusen ◽  
Paul Kögerler ◽  
Wolfgang Bensch
Keyword(s):  
Mass Spectra ◽  
Three Dimensional ◽  
Exchange Interactions ◽  
Antiferromagnetic Exchange ◽  
Orthorhombic Space Group ◽  
Linear Chains ◽  
Dimensional Network ◽  
Vis Spectroscopy ◽  
Anionic Cluster ◽  
Solvothermal Conditions

Abstract The compound {[Cu(C5H14N2)2]3[V15As6O42(H2O)]} was synthesized under solvothermal conditions. During the reaction the VV species of NH4VO3 are reduced to VIV providing the 15 reduced VIV centers in the anionic cluster. The compound crystallizes in the non-centrosymmetric orthorhombic space group P212121 with four formula units in the cell, V =9464:8(4) Å3. The structure features [V15As6O42(H2O)]6- anions which are joinded by Cu2+-centered complexes to form linear chains. If a long Cu-O bond is considered as weak intermolecular interaction a three-dimensional network is generated. The compound is partially soluble in water as evidenced by UV/Vis spectroscopy and mass spectra. The magnetic susceptibility of the compound is dominated by strong intra-cluster antiferromagnetic exchange interactions.

Antiferromagnetic exchange in manganese(II) monophenylphosphinate and the effects of cadmium doping

1989 ◽  
Vol 67 (7) ◽  
pp. 1239-1243 ◽  
Author(s):  
Jlng-Long Du ◽  
Robert C. Thompson
Keyword(s):  
Magnetic Susceptibility ◽  
Theoretical Models ◽  
Magnetic Data ◽  
Coupling Constant ◽  
Scanning Calorimetry ◽  
Manganese Compound ◽  
Linear Chains ◽  
Magnetic Chain ◽  
Metal Materials ◽  
Polymeric Structures

Mn[H(C6H5)PO2]2, its cadmium analogue, and mixed metal materials of composition Mn1−xCdx[H(C6H5)PO2]2 (x = 0.005, 0.01, 0.09, 0.27, and 0.47) have been synthesized and characterized by X-ray powder diffraction, infrared spectroscopy, differential scanning calorimetry and low-temperature (4.2 to 80 K) magnetic susceptibility studies. The materials are shown to be isomorphous and are considered to have polymeric structures in which chains of metal atoms are linked by bridging phosphinate groups. The pure manganese compound is antiferromagnetic (maximum in xm at ~35 K) and the magnetic data for the compound have been analyzed according to two theoretical models for linear chains of antiferromagnetically coupled manganese(II) (d5, spin-free) ions. The Wagner and Friedberg model gives J = −3.00 cm−1 and the Weng model gives J = −2.78 cm−1. The effects of replacing Mn2+ by Cd2+ ions in the polymer is to increase the magnetic susceptibility (per mol of Mn) at all temperatures. Analysis of the data as a function of Cd doping indicates the incorporation of a paramagnetic component to the susceptibility which increases with increasing Cd content. In addition, the absolute value of the exchange coupling constant appears to decrease as the Cd content increases. These effects are considered in terms of a random defect model in which the replacement of Mn ions in the polymer by Cd ions results in the formation of Cd ion separated finite magnetic chain fragments. Keywords: manganese(II) monophenylphosphinate, magnetic properties, coordination polymer, cadmium doped antiferromagnet.

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.

Transition metal azolates from metallocenes. Part 3: Polymeric manganese(II) and nickel(II) pyrazolates; synthesis, characterization, and magnetochemistry

1998 ◽  
Vol 76 (8) ◽  
pp. 1130-1137 ◽  
Author(s):  
Alan Storr ◽  
David A Summers ◽  
Robert C Thompson
Keyword(s):  
Metal Ions ◽  
Exchange Coupling ◽  
Variable Temperature ◽  
Indirect Evidence ◽  
Inert Atmosphere ◽  
Magnetic Data ◽  
Antiferromagnetic Coupling ◽  
Coupling Constant ◽  
Direct Reactions ◽  
Nickel Manganese

Direct reactions of nickelocene and manganocene with molten pyrazoles in an inert atmosphere or under vacuum have led to the isolation of the following metal pyrazolate compounds: [Ni(4-Xpz)2]x (where X = H, Cl and pz = pyrazolate); [M(4-Xdmpz)2]x (where X = H, CH3, Cl, Br and M = Ni, Mn anddmpz = 3,5-dimethylpyazolate); and [Mn(4-Xpz)2(4-XpzH)]x (where X = Cl, Br and pzH = pyrazole). On the basis of indirect evidence all compounds are considered to have extended chain structures with metal ions linked in chains by double bridging pyrazolates. The two [Ni(4-Xpz)2]x compounds are diamagnetic while all others are paramagnetic. Variable temperature magnetic susceptibility studies on the paramagnetic compounds reveal antiferromagnetic coupling between neighbouring metal ions. Analysis of the magnetic data (Hamiltonian of the form H = -2J sum Si·Sj) yields values of the exchange coupling constant J of -14 to -17 cm -1for the [Ni(4-Xdmpz)2]x compounds, -1.2 to -2.1 cm-1 for the [Mn(4-Xdmpz)2]x compounds, and -0.41 cm-1 for the [Mn(4-Xpz)2(4-XpzH)]x compounds.Key words: nickel, manganese, manganocene, nickelocene, pyrazolates, antiferromagnetic exchange.

Probing through-space and through-bond magnetic exchange couplings in a new benzotriazinyl radical and its metal complexes

2019 ◽  
Vol 48 (37) ◽  
pp. 14189-14200 ◽  
Author(s):  
Rajendar Nasani ◽  
Thulaseedharan Nair Sailaja Sidharth ◽  
Subhadip Roy ◽  
Arpan Mondal ◽  
Jeremy M. Rawson ◽  
...  
Keyword(s):  
Metal Complexes ◽  
Exchange Coupling ◽  
Ferromagnetic Metal ◽  
Antiferromagnetic Exchange ◽  
Magnetic Exchange ◽  
Radical Coupling ◽  
Metal Radical

A new Blatter radical and its Zn(ii) (1), Ni(ii) (2) and Co(ii) (3) complexes were isolated. Complex 1 exhibited radical⋯radical antiferromagnetic exchange coupling, whereas complexes 2 and 3 showed ferromagnetic metal–radical coupling.

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