Reduction and spin transition of some macrocyclic Fe(III) complexes

1984 ◽  
Vol 49 (11) ◽  
pp. 2579-2585
Author(s):  
Dana M. Wagnerová ◽  
Pavel Stopka ◽  
Günter Lassmann ◽  
Bernd Ebert
Keyword(s):  
Catalytic Activity ◽  
Spin Transition ◽  
Spin States ◽  
Monomeric Form ◽  
Esr Spectrum

The ESR and absorption spectroscopies were used to study the reduction of Fe(III) tetrasulphophthalocyanine (FeTSP) and Fe(III) chloro-deuteroporphyrin (FeCDP) by ascorbic acisd and cysteine. Only the monomeric form of Fe(III)TSP gives an ESR spectrum, while the dimer is ESR quiet. The complex is low-spin, and is rapidly reduced by both substrates to Fe(II)TSP. The spin states of the complexes are correlated with their catalytic activity in the oxidation of the substrates by dioxygen.

scholarly journals Elastic Origin of the Unsymmetrical Thermal Hysteresis in Spin Crossover Materials: Evidence of Symmetry Breaking

Symmetry ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 828
Author(s):  
Mamadou Ndiaye ◽  
Nour El Islam Belmouri ◽  
Jorge Linares ◽  
Kamel Boukheddaden
Keyword(s):  
Symmetry Breaking ◽  
High Spin ◽  
Spin Crossover ◽  
Thermal Hysteresis ◽  
Spin Transition ◽  
Hysteresis Loops ◽  
Point Of View ◽  
Self Organization ◽  
Spin States ◽  
Heating And Cooling

The jungle of experimental behaviors of spin-crossover materials contains a tremendous number of unexpected behaviors, among which, the unsymmetrical hysteresis loops having different shapes on heating and cooling, that we often encounter in literature. Excluding an extra effect of crystallographic phase transitions, we study here these phenomena from the point of view of elastic modeling and we demonstrate that a simple model accounting for the bond lengths misfits between the high-spin and low-spin states is sufficient to describe the situation of unsymmetrical hysteresis showing plateaus at the transition only on cooling or on heating branches. The idea behind this effect relates to the existence of a discriminant elastic frustration in the lattice, which expresses only along the high-spin to low-spin transition or in the opposite side. The obtained two-step transitions showed characteristics of self-organization of the spin states under the form of stripes, which we explain as an emergence process of antagonist directional elastic interactions inside the lattice. The analysis of the spin state transformation inside the plateau on cooling in terms of two sublattices demonstrated that the elastic-driven self-organization of the spin states is accompanied with a symmetry breaking.

scholarly journals Five 2,6-Di(pyrazol-1-yl)pyridine-4-carboxylate Esters, and the Spin States of their Iron(II) Complexes

2019 ◽  
Vol 5 (1) ◽  
pp. 9 ◽  
Author(s):  
Iurii Galadzhun ◽  
Rafal Kulmaczewski ◽  
and Malcolm A. Halcrow
Keyword(s):  
Room Temperature ◽  
Spin Crossover ◽  
Thermal Hysteresis ◽  
Spin Transition ◽  
Benzyl Ester ◽  
The Other ◽  
Spin States ◽  
Phenyl Ester ◽  
Coupling Reagent ◽  
Complex Salts

Two phenyl ester and three benzyl ester derivatives have been synthesized from 2,6-di(pyrazol-1-yl)pyridine-4-carboxylic acid and the appropriate phenyl or benzyl alcohol using N,N’-dicyclohexylcarbodiimide as the coupling reagent. Complexation of the ligands with Fe[BF4]2·6H2O in acetone yielded the corresponding [FeL2][BF4]2 complex salts. Four of the new ligands and four of the complexes have been crystallographically characterised. Particularly noteworthy are two polymorphs of [Fe(L3)2][BF4]2·2MeNO2 (L3 = 3,4-dimethoxyphenyl 2,6-di{pyrazol-1-yl}pyridine-4-carboxylate), one of which is crystallographically characterised as high-spin while the other exhibits the onset of spin-crossover above room temperature. The other complexes are similarly low-spin at low temperature but exhibit gradual spin-crossover on heating, except for an acetone solvate of [Fe(L5)2][BF4]2 (L5 = benzyl 2,6-di{pyrazol-1-yl}pyridine-4-carboxylate), which exhibits a more abrupt spin-transition at T½ = 273 K with 9 K thermal hysteresis.

scholarly journals Molecular S = 2 High-Spin, S = 0 Low-Spin and S = 0 ⇄ 2 Spin-Transition/-Crossover Nickel(II)-Bis(nitroxide) Coordination Compounds

Inorganics ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 10
Author(s):  
Takayuki Ishida ◽  
Saki Ito ◽  
Yuta Homma ◽  
Yukiya Kyoden
Keyword(s):  
High Spin ◽  
Density Functional ◽  
Coupling Parameter ◽  
Spin Transition ◽  
Coordination Bond ◽  
Antiferromagnetic Coupling ◽  
Temperature Phase ◽  
Spin States ◽  
Coordination Structure ◽  
Nickel Ion

Heterospin systems have a great advantage in frontier orbital engineering since they utilize a wide diversity of paramagnetic chromophores and almost infinite combinations and mutual geometries. Strong exchange couplings are expected in 3d–2p heterospin compounds, where the nitroxide (aminoxyl) oxygen atom has a direct coordination bond with a nickel(II) ion. Complex formation of nickel(II) salts and tert-butyl 2-pyridyl nitroxides afforded a discrete 2p–3d–2p triad. Ferromagnetic coupling is favored when the magnetic orbitals, nickel(II) dσ and radical π*, are arranged in a strictly orthogonal fashion, namely, a planar coordination structure is characterized. In contrast, a severe twist around the coordination bond gives an orbital overlap, resulting in antiferromagnetic coupling. Non-chelatable nitroxide ligands are available for highly twisted and practically diamagnetic complexes. Here, the Ni–O–N–Csp2 torsion (dihedral) angle is supposed to be a useful metric to describe the nickel ion dislocated out of the radical π* nodal plane. Spin-transition complexes exhibited a planar coordination structure in a high-temperature phase and a nonplanar structure in a low-temperature phase. The gradual spin transition is described as a spin equilibrium obeying the van’t Hoff law. Density functional theory calculation indicates that the energy level crossing of the high- and low-spin states. The optimized structures of diamagnetic and high-spin states well agreed with the experimental large and small torsions, respectively. The novel mechanism of the present spin transition lies in the ferro-/antiferromagnetic coupling switch. The entropy-driven mechanism is plausible after combining the results of the related copper(II)-nitroxide compounds. Attention must be paid to the coupling parameter J as a variable of temperature in the magnetic analysis of such spin-transition materials. For future work, the exchange coupling may be tuned by chemical modification and external stimulus, because it has been clarified that the parameter is sensitive to the coordination structure and actually varies from 2J/kB = +400 K to −1400 K.

Isomorphism between the electro-elastic modeling of the spin transition and Ising-like model with competing interactions: Elastic generation of self-organized spin states

2021 ◽  
Vol 129 (15) ◽  
pp. 153901
Author(s):  
Mamadou Ndiaye ◽  
Yogendra Singh ◽  
Houcem Fourati ◽  
Mouhamadou Sy ◽  
Bassirou Lo ◽  
...  
Keyword(s):  
Spin Transition ◽  
Spin States ◽  
Competing Interactions ◽  
Self Organized

scholarly journals Compressional behavior and spin state of δ-(Al,Fe)OOH at high pressures

2019 ◽  
Vol 104 (9) ◽  
pp. 1273-1284 ◽  
Author(s):  
Itaru Ohira ◽  
Jennifer M. Jackson ◽  
Natalia V. Solomatova ◽  
Wolfgang Sturhahn ◽  
Gregory J. Finkelstein ◽  
...  
Keyword(s):  
Solid Solution ◽  
Spin Crossover ◽  
High Pressures ◽  
Spin Transition ◽  
Heterogeneous Structure ◽  
Spin States ◽  
Hydrogen Transport ◽  
Crossover Region ◽  
Volume Collapse ◽  
Deep Interior

Abstract Hydrogen transport from the surface to the deep interior and distribution in the mantle are important in the evolution and dynamics of the Earth. An aluminum oxy-hydroxide, δ-AlOOH, might influence hydrogen transport in the deep mantle because of its high stability extending to lower mantle conditions. The compressional behavior and spin states of δ-(Al,Fe3+)OOH phases were investigated with synchrotron X-ray diffraction and Mössbauer spectroscopy under high pressure and room temperature. Pressure-volume (P-V) profiles of the δ-(Al0.908(9)57Fe0.045(1))OOH1.14(3) [Fe/(Al+Fe) = 0.047(10), δ-Fe5] and the δ-(Al0.832(5)57Fe0.117(1))OOH1.15(3) [Fe/(Al+Fe) = 0.123(2), δ-Fe12] show that these hydrous phases undergo two distinct structural transitions involving changes in hydrogen bonding environments and a high- to low-spin crossover in Fe3+. A change of axial compressibility accompanied by a transition from an ordered (P21nm) to disordered hydrogen bond (Pnnm) occurs near 10 GPa for both δ-Fe5 and δ-Fe12 samples. Through this transition, the crystallographic a and b axes become stiffer, whereas the c axis does not show such a change, as observed in pure δ-AlOOH. A volume collapse due to a transition from high- to low-spin states in the Fe3+ ions is complete below 32–40 GPa in δ-Fe5 and δ-Fe12, which i ~10 GPa lower than that reported for pure ε-FeOOH. Evaluation of the Mössbauer spectra of δ-(Al0.824(10)57Fe0.126(4))OOH1.15(4) [Fe/(Al+Fe) = 0.133(3), δ-Fe13] also indicate a spin transition between 32–45 GPa. Phases in the δ-(Al,Fe)OOH solid solution with similar iron concentrations as those studied here could cause an anomalously high ρ/νΦ ratio (bulk sound velocity, defined as K/ρ at depths corresponding to the spin crossover region (~900 to ~1000 km depth), whereas outside the spin crossover region a low ρ/νΦ anomaly would be expected. These results suggest that the δ-(Al,Fe)OOH solid solution may play an important role in understanding the heterogeneous structure of the deep Earth.

scholarly journals The catalytic activity of monomeric yeast hexokinase A

1977 ◽  
Vol 161 (1) ◽  
pp. 181-183
Author(s):  
B P Yip ◽  
F B Rudolph
Keyword(s):  
Catalytic Activity ◽  
Monomeric Form ◽  
Catalytically Active ◽  
Yeast Hexokinase

It has been suggested [Williams, D.C. & Jones, J.G. (1976) Biochem. J. 155, 661-667] that monomeric hexokinase isoenzyme A is not catalytically active. We here present data from reacting-enzyme sedimentation, dissociation experiments and from previous studies which are consistent with the monomeric form possessing catalytic activity.

High resolution electron microscopy of lanthanum phosphate crystals

1978 ◽  
Vol 36 (1) ◽  
pp. 274-275
Author(s):  
J. C. Wheatley ◽  
J. M. Cowley
Keyword(s):  
Electron Microscopy ◽  
Catalytic Activity ◽  
High Resolution ◽  
Petroleum Industry ◽  
High Resolution Electron Microscopy ◽  
Lanthanum Phosphate ◽  
Good Catalyst ◽  
Resolution Electron ◽  
Good Catalytic Activity ◽  
Physical And Chemical

Rare-earth phosphates are of particular interest because of their catalytic properties associated with the hydrolysis of many aromatic chlorides in the petroleum industry. Lanthanum phosphates (LaPO4) which have been doped with small amounts of copper have shown increased catalytic activity (1). However the physical and chemical characteristics of the samples leading to good catalytic activity are not known.Many catalysts are amorphous and thus do not easily lend themselves to methods of investigation which would include electron microscopy. However, the LaPO4, crystals are quite suitable samples for high resolution techniques.The samples used were obtained from William L. Kehl of Gulf Research and Development Company. The electron microscopy was carried out on a JEOL JEM-100B which had been modified for high resolution microscopy (2). Standard high resolution techniques were employed. Three different sample types were observed: 669A-1-5-7 (poor catalyst), H-L-2 (good catalyst) and 27-011 (good catalyst).

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