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.

Synthesis, spectroscopic and magnetic properties of some pyrazine-bridged iron(II) sulfonate complexes

1988 ◽  
Vol 66 (8) ◽  
pp. 2079-2087 ◽  
Author(s):  
John S. Haynes ◽  
John R. Sams ◽  
Robert C. Thompson
Keyword(s):  
Heisenberg Model ◽  
Hyperfine Splitting ◽  
Variable Temperature ◽  
Magnetic Data ◽  
Antiferromagnetic Coupling ◽  
Antiferromagnetic Exchange ◽  
Two Dimensional ◽  
Scanning Calorimetry ◽  
Best Fit ◽  
Magnetic Hyperfine Splitting

Six new pyrazine-bridged complexes of iron(II) have been prepared and studied using magnetic susceptibility, differential scanning calorimetry, and vibrational, electronic, and Mössbauer spectroscopic methods. Fe(pyz)(CF3SO3)2 exhibits a susceptibility maximum at 4.4 K and analysis of the magnetic data according to a two-dimensional S = 2 system in the (isotropic) Heisenberg limit yields best-fit values of J = −0.26 cm−1 and g = 2.20. Variable temperature Mössbauer spectra between 4.2 and 1.6 K are also reported for this compound and show the onset of magnetic hyperfine splitting below ~3.8 K. Analysis of magnetic data for Fe(pyz)2(CH3SO3)2 and Fe(pyz)2(CF3SO3)2•CH3OH according to the two-dimensional Heisenberg model also indicates the presence of weak antiferromagnetic exchange in these complexes (J = −0.18 and −0.20 cm−1, respectively). No clear evidence for magnetic concentration was obtained from our studies on Fe(pyz)2(CIO4)2, Fe(pyz)(p-CH3C6H4SO3)2, and Fe(pyz)(p-CH3C6H4SO3)2•2CH3OH; any antiferromagnetic coupling in these complexes must be considerably weaker than in the other complexes studied.

Polynuclear pyrazolate complexes of copper. Crystal and molecular structures of [Cu(tmpz)]3, [Cu(3-CO2dmpz)(tmpzH)]2Cu, and [Cu(4-Br-3-CO2mepz)(4-Br-dmpzH)2]2 (where mepz = methylpyrazolate, dmpz = dimethylpyrazolate, and tmpz = trimethylpyrazolate) and magnetic susceptibility studies on the dinuclear complex

1992 ◽  
Vol 70 (8) ◽  
pp. 2161-2173 ◽  
Author(s):  
Martin K. Ehlert ◽  
Steven J. Rettig ◽  
Alan Storr ◽  
Robert C. Thompson ◽  
James Trotter
Keyword(s):  
Magnetic Susceptibility ◽  
Exchange Coupling ◽  
Bulk Sample ◽  
Molecular Structures ◽  
Antiferromagnetic Coupling ◽  
Coupling Constant ◽  
Copper Metal ◽  
Copper Crystal ◽  
Space Group ◽  
Crystalline Forms

The reaction of molten trimethylpyrazole (tmpzH) with copper metal shot in air yields a mixture of the trinuclear copper(I) complex [Cu(tmpz)]3, 1, and the trinuclear copper(I/II) complex [Cu(3-CO2dmpz)(tmpzH)]2Cu, 2 (where dmpz is dimethylpyrazolate). Crystals of 1 are monoclinic, a = 8.403(3), b = 22.453(2), c = 11.362(2) Å, (3 = 95.83(2)°, Z = 4, space group P21/c. Crystals of 2 are triclinic, a = 10.988(3), b = 11.009(2), c = 6.457(1) Å, α = 103.13(2)°, β = 103.02(2)°, γ = 108.70(2)°, Z = 1, space group [Formula: see text]. The reaction of molten 4-bromodimethylpyrazole (4-BrdmpzH) with copper metal shot in air gave the binuclear copper(II) complex [Cu(4-Br-3-CO)2mepz)(4-BrdmpzH)2]2, 3 (where mepz is methylpyrazolate). There are two crystalline forms of 3:3a, triclinic, a = 10.152(3), b = 13.068(3), c = 10.033(3) Å, a = 112.38(2)°, (3 = 116.46(2)°, γ = 70.29(2)°, Z = 1, space group [Formula: see text]; and 3b, monoclinic, a = 13.470(1), b = 16.005(2), c = 20.174(1) Å, β = 98.142(6)°, Z = 4, space group C2/c. Magnetic susceptibility studies on a bulk sample of 3 (2.0–300 K) revealed antiferromagnetic coupling between the double pyrazolate bridged copper centres and analysis of the data according to a Heisenberg model for coupled pairs of S = 1/2 metal ions gave −75.4 cm−1 for the value of the exchange coupling constant, J. The crystal structures of 1, 2, 3a, and 3b were solved by the Patterson method and were refined by full-matrix least-squares procedures to final R values of 0.036, 0.056, 0.042, and 0.042 for 2265, 1764, 2011, and 2575 reflections with I ≥ 3σ(I), respectively.

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.

scholarly journals Assessment of density functional approximations for calculation of exchange coupling constants in thiocyanato and cyanato double bridged binuclear Ni(II) complexes

2020 ◽  
pp. 71-71
Author(s):  
Matija Zlatar ◽  
Filip Vlahovic ◽  
Dragana Mitic ◽  
Mario Zlatovic ◽  
Maja Gruden
Keyword(s):  
Magnetic Properties ◽  
Exchange Coupling ◽  
Density Functional ◽  
Coupling Constants ◽  
Antiferromagnetic Coupling ◽  
Binuclear Complexes ◽  
Coupling Constant ◽  
Symmetry Approach ◽  
Experimental Values ◽  
Broken Symmetry Approach

In the present work, we examine the magnetic properties of 8 "endto-end" thiocyanato, and 3 "end-to-end" cyanato double bridged Ni(II) binuclear complexes. Thiocyanato complexes are weakly ferromagnetic. Cyanato bridged complexes exhibit weak antiferromagnetic coupling. Therefore, it is a challenge for computational chemistry to calculate the exchange coupling constant in these systems accurately. 17 different Density Functional Approximations with different flavors are used to find the method of choice to study magnetic properties in binuclear Ni(II) complexes within the Broken-Symmetry approach. It is found that M06-2X and PWPB95 performed the best compared to experimental values for the entire set of examined complexes. Furthermore, the magneto-structural correlation rationalizes the results.

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 3. Synthesis and study of Cu(I) and Cu(II) complexes of 4-Xdmpz (where X = H, Cl, Br, I, and CH3 for Cu(I) and X = H, Cl, Br, and CH3 for Cu(II); dmpz = 3,5-dimethylpyrazolate)

1992 ◽  
Vol 70 (4) ◽  
pp. 1121-1128 ◽  
Author(s):  
Martin K. Ehlert ◽  
Alan Storr ◽  
Robert C. Thompson
Keyword(s):  
Magnetic Susceptibility ◽  
Spectroscopic Studies ◽  
Magnetic Data ◽  
Antiferromagnetic Coupling ◽  
Polymeric Chain ◽  
Differential Scanning Calorimetric ◽  
Scanning Electron Micrographs ◽  
Coupling Constant ◽  
Abrupt Decrease ◽  
Calorimetric Studies

The copper(I) complexes [Cu(4-Xdmpz)]3 (where X = H, Cl, Br, I and CH3; dmpz = 3,5-dimethylpyrazolate) and the copper(II) complexes [Cu(4-Xdmpz)2]x have been synthesized and characterized. Qualitative solubility, infrared spectroscopic, and differential scanning calorimetric studies are reported for all complexes. Mass spectra support trimeric formulations for the copper(I) complexes. Scanning electron micrographs and powder X-ray diffractograms have been recorded for the copper(II) compounds. Electronic and EPR spectroscopic studies as well as magnetic susceptibility studies from 2 to 300 K are also reported for the copper(II) compounds, which are proposed to have polymeric chain structures. The magnetic data reveal strong antiferromagnetic interactions in all four of the copper(II) compounds. The data have been analysed employing an isotropic Heisenberg model for antiferromagnetic coupling in extended chain polymers. Values of the exchange coupling constant, J, are determined as −58, −61, −66, and −66 cm−1 for the X = H, CH3, Cl, and Br complexes respectively. The X = Cl compound exhibits an abrupt decrease in magnetic susceptibility below 40 K and possible causes of this anomalous behaviour are discussed.

Assessing the Calculation of Exchange Coupling Constants and Spin Crossover Gaps Using the Approximate Projection Model to Improve Density Function Calculations

2019 ◽  
Author(s):  
Xianghai Sheng ◽  
Lee Thompson ◽  
Hrant Hratchian
Keyword(s):  
Density Functional Theory ◽  
Exchange Coupling ◽  
Density Functional ◽  
Spin Crossover ◽  
Coupling Constants ◽  
Spin Projection ◽  
Coupling Constant ◽  
Projection Model ◽  
Functional Theory

This work evaluates the quality of exchange coupling constant and spin crossover gap calculations using density functional theory corrected by the Approximate Projection model. Results show that improvements using the Approximate Projection model range from modest to significant. This study demonstrates that, at least for the class of systems examined here, spin-projection generally improves the quality of density functional theory calculations of J-coupling constants and spin crossover gaps. Furthermore, it is shown that spin-projection can be important for both geometry optimization and energy evaluations. The Approximate Project model provides an affordable and practical approach for effectively correcting spin-contamination errors in molecular exchange coupling constant and spin crossover gap calculations.

Exchange Coupling of Transition-Metal Ions through Hydrogen Bonding:  A Theoretical Investigation

2002 ◽  
Vol 124 (18) ◽  
pp. 5197-5205 ◽  
Author(s):  
Cédric Desplanches ◽  
Eliseo Ruiz ◽  
Antonio Rodríguez-Fortea ◽  
Santiago Alvarez
Keyword(s):  
Hydrogen Bonding ◽  
Transition Metal ◽  
Metal Ions ◽  
Theoretical Investigation ◽  
Exchange Coupling ◽  
Transition Metal Ions

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.

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