scholarly journals Spin orientation switching in layered perovskite oxyfluoride Pb3Fe2O5F2

2021 ◽  
Author(s):  
Kengo Oka ◽  
Yusuke Nambu ◽  
Masayuki Ochi ◽  
Naoaki Hayashi ◽  
Yoshihiro Kusano ◽  
...  
Keyword(s):  
Magnetic Moments ◽  
Magnetic Interaction ◽  
Molecular Magnets ◽  
Spin Reorientation ◽  
Layered Perovskite ◽  
Ligand Field ◽  
Spin Orientation ◽  
Coordination Environment ◽  
Splitting Energy ◽  
Homo Lumo

Abstract Control of spin alignment in magnetic materials is crucial for developing switching devices. In molecular magnets, magnetic anisotropy can be rationally controlled by varying their ligands that allow tuning of ligand field splitting energy. However, the inherent weak magnetic interaction between spins or spin-cluster results in spin reorientation (SR) occurring only at low temperatures. Here, we show that layered perovskite oxyfluoride Pb3Fe2O5F2 exhibits a SR transition at 380 K, with the magnetic moments changing from perpendicular to parallel to the c-axis. It is found that the SR is caused by a ferroelectric-like phase transition, where the magnetic HOMO-LUMO interaction changes upon the structural transition due to the concerted effect of the heteroleptic FeO5F coordination and the steric effect of Pb. This finding indicates that the design of spin orientation by local coordination environment, which is common in molecular magnets, can be extended to extended oxides by introducing different anions.

scholarly journals Ligand Field Effects on the Ground and Excited States of the Catalytically Active FeO2+ Species

2018 ◽  
Author(s):  
Justin K. Kirkland ◽  
Shahriar N. Khan ◽  
Bryan Casale ◽  
Evangelos Miliordos ◽  
Konstantinos Vogiatzis
Keyword(s):  
Excited States ◽  
Function Theory ◽  
Weak Field ◽  
Ligand Field ◽  
Model Complexes ◽  
Coordination Environment ◽  
Reactivity Descriptors ◽  
Field Effects ◽  
Catalytically Active ◽  
High Level

<p>We have performed high-level wave function theory calculations on bare FeO2+ and a series of non-heme Fe(IV)-oxo model complexes in order to elucidate the electronic properties and the ligand field effects on those channels. Our results suggest that a coordination environment formed by a weak field gives access to both competitive channels, yielding more reactive Fe(IV)-oxo sites. On the contrary, a strong ligand environment stabilizes only the σ-channel. Our concluding remarks will aid on the derivation of new structure-reactivity descriptors that can contribute on the development of the next generation of functional catalysts.</p>

scholarly journals Ligand Field Effects on the Ground and Excited States of the Catalytically Active FeO2+ Species

2018 ◽  
Author(s):  
Justin K. Kirkland ◽  
Shahriar N. Khan ◽  
Bryan Casale ◽  
Evangelos Miliordos ◽  
Konstantinos Vogiatzis
Keyword(s):  
Excited States ◽  
Function Theory ◽  
Weak Field ◽  
Ligand Field ◽  
Model Complexes ◽  
Coordination Environment ◽  
Reactivity Descriptors ◽  
Field Effects ◽  
Catalytically Active ◽  
High Level

<p>We have performed high-level wave function theory calculations on bare FeO2+ and a series of non-heme Fe(IV)-oxo model complexes in order to elucidate the electronic properties and the ligand field effects on those channels. Our results suggest that a coordination environment formed by a weak field gives access to both competitive channels, yielding more reactive Fe(IV)-oxo sites. On the contrary, a strong ligand environment stabilizes only the σ-channel. Our concluding remarks will aid on the derivation of new structure-reactivity descriptors that can contribute on the development of the next generation of functional catalysts.</p>

Magnetism, electronic spectra, and structure of transition metal alkoxides. I. methoxides and ethoxides of chromium(II), manganese(II), Iron(II), cobalt(II), nickel(II), copper(II), titanium(III), chromium(III), and iron(III)

1966 ◽  
Vol 19 (2) ◽  
pp. 207 ◽  
Author(s):  
RW Adams ◽  
E Bishop ◽  
RL Martin ◽  
G Winter
Keyword(s):  
Transition Metal ◽  
Spectral Data ◽  
Electronic Spectra ◽  
Magnetic Moments ◽  
Field Parameter ◽  
Ligand Field ◽  
Metal Alkoxides ◽  
Infinite Lattices ◽  
Ligand Field Parameter

The magnetic moments and electronic spectra are reported for the following divalent transition metal methoxides: Cr(OCH3)2, Mn(OCH3)2, Fe(OCH3)2, Co(OCH3)2, Ni(OCH3)2, and Cu(OCH3)2. These measurements when coupled with the involatility and insolubility of the compounds favour structures based on infinite lattices composed either of regular (Mn, Fe, Co, and Ni) or distorted (Cr and Cu) MO6 octahedra. The spectral data place the ligand field parameter, Δ, for the methoxide group very close to that of water.

Atomic structure and physical properties of fused porphyrin nanoclusters

2014 ◽  
Vol 18 (07) ◽  
pp. 552-568 ◽  
Author(s):  
Pavel V. Avramov ◽  
Alex A. Kuzubov ◽  
Seiji Sakai ◽  
Manabu Ohtomo ◽  
Shiro Entani ◽  
...  
Keyword(s):  
Self Assembly ◽  
Electronic Structures ◽  
Ligand Field ◽  
Spin States ◽  
Cubic Symmetry ◽  
Potential Barriers ◽  
High Spin States ◽  
Formation Energies ◽  
Homo Lumo ◽  
Mechanical Rupture

The atomic and electronic structures, mechanical properties and potential barriers of formation of a set of meso–meso β–β fused porphyrin/metalloporphyrin nanopages, nanotapes, nanotubes and 2D nanofabrics were studied by GGA LC-DFT technique using cluster and PBC models. The porphyrin pages of the nanoclusters are connected with each other by graphene fragments formed by meso–meso β–β links. Fusion of all the edges of six porphyrin/metalloporphyrin units produces a novel ~ 1 nm sized molecule of cubic symmetry with a hollow cage inside. It was found that all studied nanoclusters are metastable with formation energies 0.36–7.57 kcal/mol per atom. Under applied mechanical stress, the nanoclusters exhibit superelastic and ultrastrong properties with binding graphene fragments being the weakest links for mechanical rupture. Depending on the spin-dependent reaction pathways, the hollow caged nanoclusters exhibit almost zero or low potential energy barriers (1–10 kcal/mol) during the initial stages of self-assembly. All nanoclusters exibit the main features of the electronic structures of the parent porphyrins, in particular the nature of HOMO/LUMO states and the relative energetic positions of the metal d states. The induced curvature of the hollow cage nanoclusters leads to admixture of more than 2% of the dπ⊥ states to the dσ energy region and formation of vacant superatomic molecular orbitals of d character in cubic ligand field. The Fe -derived hollow-caged nanoclusters reveal extremely high spin states with small energy differences between ferromagnetic and antiferromagnetic configurations, which can be utilized for quantum holonomic computations.

Cobalt(II), nickel(II) and copper(II) complexes of some 2'-hydroxychalcones

1980 ◽  
Vol 33 (4) ◽  
pp. 737 ◽  
Author(s):  
M Palaniandavar ◽  
C Natarajan
Keyword(s):  
Infrared Spectra ◽  
Metal Ion ◽  
Magnetic Moments ◽  
Phenyl Group ◽  
Ligand Field ◽  
Square Planar ◽  
Spin Pairing ◽  
Square Configuration ◽  
Electron Sink ◽  
Octahedral Configuration

Metal(II) bis-chelates of the type ML2 [M = CoII, NiII, CuII; L = 2'- hydroxy-5'-X-chalcone where X = H, CH3, Cl] have been prepared and studied. Structures have been assessed by the measurement of magnetic moments, ligand field and infrared spectra and thermal properties. These chelates possess low-spin trans-square-planar configuration and show resistance to adduct formation in contrast to metal(II) chelates of β-diketones, salicylaldehyde, o-hydroxyaryl ketones and esters and o-hydroxy-crotonophenones, which have high-spin octahedral configuration. Extensive conjugation lowers the energy of the π3* orbital which enters into a very strong dπ-π3* interaction leading to spin-pairing. ��� Infrared spectra indicate that the carbonyl group is perturbed only slightly by coordination to metal. A change in metal ion affects v(C=O), v(M-O) and other vibrations and the order of stability, namely, Co ≈ Ni < Cu, inferred from these vibrations is as expected for the low-spin square configuration of the chelates. Introduction of substituents (5'-X) alters only v(M-O) significantly and the order of stability, namely, Cl > CH3 > H, derived from v(M-O) is consistent with Taft's resonance polar parameters of the substituents. All these observations are explained by the electron sink property of the phenyl group.

scholarly journals Electric polarization from spiral order below 200K in multiferroic YBaCuFeO5

2014 ◽  
Vol 70 (a1) ◽  
pp. C388-C388
Author(s):  
Mickael Morin ◽  
Denis Scheptyakov ◽  
Lukas Keller ◽  
Juan Rodríguez-Carvajal ◽  
Andrea Scaramucci ◽  
...  
Keyword(s):  
Magnetic Order ◽  
Magnetic Moments ◽  
Double Perovskite ◽  
Electric Polarization ◽  
Ferroelectric Materials ◽  
Point Of View ◽  
Spin Reorientation ◽  
Magnetic Interactions ◽  
Practical Applications ◽  
Spiral Model

Ferroelectric materials have been known for almost one century [1]. While their potential for applications was rapidly recognized, the possibility of combining ferroelectricity with magnetic order -preferably with ferromagnetism- has resulted in an enormous deal of interest during the last decade. Several new materials combining both types of order have been recently reported, although their promising multifunctionalities have been obscured by two facts: on one side, most of them are antiferromagnetic; on the other, their transition temperatures, typically below 40K, are too low for most practical applications. The oxygen-defficient double perovskite YBaFeCuO5 constitutes a remarkable exception. Spontaneous electric polarization has been recently reported to exist below an unusually high temperature of TC ≍ 200K [2] coinciding with the occurrence of a commensurate - to - incommensurate reorientation of the Fe3+ and Cu2+ magnetic moments [3,4]. From a more fundamental point of view the observation of incommensurable magnetic order in a tetragonal material at such high temperatures is rather surprising. In particular, the nature of the relevant competing magnetic interactions and its possible link to low dimensionality or geometrical frustration is not understood at present. Although the existence of the spin reorientation in this material is known since 1995 [3] the low temperature magnetic structure has not yet been solved. Using neutron powder diffraction we have recently been able to propose a spiral model which satisfactorily describes the measured magnetic intensities below TC. Further, investigation of the crystal structure showed the existence of small anomalies in the lattice parameters and some interatomic distances at TC. The relevance of these findings for the magnetoelectric coupling, the direction of the polarization, the modification of the different exchange paths in the structure and the stabilization of the incommensurate magnetic order below TC is discussed.

HIGH ENERGY MODIFICATIONS OF THE HYDRATES OF ZINC SULFATE

1965 ◽  
Vol 43 (12) ◽  
pp. 3129-3132 ◽  
Author(s):  
J. W. S. Jamieson ◽  
R. A. Lamontagne ◽  
Barbara A. Pattern ◽  
G. R. Brown
Keyword(s):  
Zinc Sulfate ◽  
High Energy ◽  
Crystalline Form ◽  
Ligand Field ◽  
Field Splitting ◽  
Maximum Heat ◽  
Heats Of Solution ◽  
Splitting Energy ◽  
Heat Of Transition ◽  
Vacuum Dehydration

Much higher heats of solution than have previously been observed for hydrates of zinc sulfate have been measured for various new vacuum dehydration products. It is suggested that the maximum heat of transition to normal crystalline form of 82.8 cal/g, 23.8 kcal per mole of heptahydrate, or 8.3 × 103 cm−1 is a satisfactory measure of the ligand field splitting energy for the hexaaquozinc(II) ion.

Copper(II) complexes of o-hydroxyarylcarbonyl compounds

1968 ◽  
Vol 21 (3) ◽  
pp. 617 ◽  
Author(s):  
DP Graddon ◽  
GM Mockler
Keyword(s):  
Solid State ◽  
Chelate Ring ◽  
Magnetic Moments ◽  
Equilibrium Constants ◽  
Ligand Field ◽  
Infrared Band ◽  
Planar Structures ◽  
Square Planar ◽  
Inductive Effects ◽  
Ligand Field Spectra

A series of copper(11) complexes has been prepared of the type CuL2Bn, where L is an o-hydroxy-aryl-, or naphthyl-, aldehyde, ketone, or ester, B is water or 4-methylpyridine, and n = 0, 1, or 2. All these complexes have a strong infrared band in the region 1600-1660 cm-l, showing that the oxygen atoms in the chelate ring are non-equivalent ; their magnetic moments fall in the range usual for copper(11) compounds. Equilibrium constants determined for the addition of one molecule of 4-methylpyridine to the anhydrous compounds in chloroform solutions fall in the range 0.5 < k < 40 and are comparable to the constant for the addition of 4-methylpyridine to bis(acetylacetonato)copper(11) (b 2.7). Increased stability of the adducts can be associated with the inductive effects of ligand substituents. Ligand field spectra in the solid state and in solution closely resemble those of corresponding bis(acetylaoetonato)copper(11) complexes and provide evidence for square-planar structures of the anhydrous complexes and square-pyramidal structures of the 1 : 1 adducts with 4-methylpyridine or water. No evidence is available for the structures of 1 : 2 adduots which may be formed in solutions in 4-methylpyridine; these solutions are unstable, but the nature of the slow reactions which occur in these solutions is not known.

scholarly journals Synthesis, Spectral, Magnetic and Thermal Studies of the Complexes of CoIIand NiIIWith Some Bidentate and Tridentate Hydrazone Ligands

2005 ◽  
Vol 2 (1) ◽  
pp. 21-29 ◽  
Author(s):  
Chetan K. Modi ◽  
Ashwin S. Patel ◽  
Bharat T. Thaker
Keyword(s):  
Magnetic Moments ◽  
Picolinic Acid ◽  
Thermal Studies ◽  
Acid Hydrazide ◽  
Spectral Studies ◽  
Ligand Field ◽  
Conductivity Measurements ◽  
Octahedral Structure ◽  
Hydrazone Ligands ◽  
Ligand Field Parameters

The reaction of Co(NO3)2.6H2O and Ni(NO3)2.6H2O with hydrazones derived from 1-phenyl-3-methyl-4-acyl-5-pyrazolone (where acyl = acetyl, propionyl, butyryl and benzoyl) with 2-picolinic acid hydrazide have been studied and characterized on the basis of elemental analysis, magnetic moments, molar conductivity measurements, IR and electronic spectral studies and thermogravimetric analysis. Various ligand field parameters have been calculated. Electronic spectral data and the magnetic moment values suggest an octahedral structure for all cobalt(II) and nickel(II) complexes.

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