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Spin Crossover (SCO) Research 2020

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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Inorganic Chemistry".

Deadline for manuscript submissions: closed (1 December 2020) | Viewed by 18249

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Special Issue Editor

Prof. Dr. Sergey G. Ovchinnikov

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Guest Editor

Kirensky Institute of Physics, Siberian Branch, Russian Academy of Sciences, Krasnoyarsk, Russia
Interests: strongly correlated electronic systems; spin crossovers in transition metal oxides; magnetism; high-temperature superconductivity

Special Issue Information

Dear Colleagues,

The awareness of the phenomenon of spin crossover dates back to almost a century ago; however, it is still attracting increasing attention from researchers in various disciplines. Two different classes of materials with spin crossover are mostly studied: metalorganic complexes and transition metal oxides. There are many common features between their physical properties in spite of the different crystallochemistry. Besides the main interest in the SCO materials for future functional electronics, spin crossover in Fe oxides under megabar pressures is important to understand the geophysical properties of the deep interiors of the Earth and other planets.

New improvements in analytical tools, manipulation and detection of nano-objects, increased computing capacities, and faster time-resolved characterization techniques are exerting a profound impact on the development of this promising field, which is seeing its range of possible applications expanded. We are offering a platform for some of this exciting new research with this promotional Special Issue of the open access journal, Molecules.

Prof. Dr. Sergey G. Ovchinnikov
Guest Editor

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Keywords

Spin crossovers in metalorganic compounds
Spin crossovers in transition metal oxides
Nonstationary effects in spin crossover materials

Published Papers (7 papers)

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Research

13 pages, 1079 KiB

Open AccessArticle

Modulation of Mn³⁺ Spin State by Guest Molecule Inclusion

by Irina A. Kühne, Kane Esien, Laurence C. Gavin, Helge Müller-Bunz, Solveig Felton and Grace G. Morgan

Molecules 2020, 25(23), 5603; https://doi.org/10.3390/molecules25235603 - 28 Nov 2020

Cited by 8 | Viewed by 3389

Abstract

Spin state preferences for a cationic Mn³⁺ chelate complex in four different crystal lattices are investigated by crystallography and SQUID magnetometry. The [MnL₁]⁺ complex cation was prepared by complexation of Mn³⁺ to the Schiff base chelate formed from condensation of 4-methoxysalicylaldehyde and 1,2-bis(3-aminopropylamino)ethane. The cation was crystallized separately with three polyatomic counterions and in one case was found to cocrystallize with a percentage of unreacted 4-methoxysalicylaldehyde starting material. The spin state preferences of the four resultant complexes [MnL₁]CF₃SO₃·xH₂O, (1), [MnL₁]PF₆·xH₂O, (2), [MnL₁]PF₆·xsal·xH₂O, (2b), and [MnL₁]BPh₄, (3), were dependent on their ability to form strong intermolecular interactions. Complexes (1) and (2), which formed hydrogen bonds between [MnL₁]⁺, lattice water and in one case also with counterion, showed an incomplete thermal spin crossover over the temperature range 5–300 K. In contrast, complex (3) with the BPh₄⁻, counterion and no lattice water, was locked into the high spin state over the same temperature range, as was complex (2b), where inclusion of the 4-methoxysalicylaldehyde guest blocked the H-bonding interaction. Full article

(This article belongs to the Special Issue Spin Crossover (SCO) Research 2020)

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10 pages, 4048 KiB

Open AccessFeature PaperArticle

Contribution of the Multiplicity Fluctuation in the Temperature Dependence of Phonon Spectra of Rare-Earth Cobaltites

by Yuri S. Orlov, Alexey E. Sokolov, Vyacheslav A. Dudnikov, Karina V. Shulga, Mikhail N. Volochaev, Sergey M. Zharkov, Nikolay P. Shestakov, Maxim A. Vysotin and Sergei G. Ovchinnikov

Molecules 2020, 25(18), 4316; https://doi.org/10.3390/molecules25184316 - 20 Sep 2020

Cited by 1 | Viewed by 2148

Abstract

We have studied, both experimentally and theoretically, the unusual temperature dependence of the phonon spectra in NdCoO₃, SmCoO₃ and GdCoO₃, where the Co³⁺ ion is in the low-spin (LS) ground state, and at the finite temperature, the [...] Read more.

n_{H S}

due to multiplicity fluctuations. We measured the absorption spectra in polycrystalline and nanostructured samples in the temperature range 3–550 K and found a quite strong breathing mode softening that cannot be explained by standard lattice anharmonicity. We showed that the anharmonicity in the electron–phonon interaction is responsible for this red shift proportional to the

n_{H S}

concentration. Full article

(This article belongs to the Special Issue Spin Crossover (SCO) Research 2020)

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17 pages, 7595 KiB

Open AccessArticle

Pressure Induced Spin Crossover and Magnetic Properties of Multiferroic Ba₃NbFe₃Si₂O₁₄

by Igor Lyubutin, Sergey Starchikov, Ivan Troyan, Yulia Nikiforova, Marianna Lyubutina and Alexander Gavriliuk

Molecules 2020, 25(17), 3808; https://doi.org/10.3390/molecules25173808 - 21 Aug 2020

Cited by 3 | Viewed by 2247

Abstract

Recently, the iron containing langasite-type crystal Ba₃NbFe₃Si₂O₁₄ has attracted great attention as a new magnetically induced multiferroic. In this work, magnetic, structural and electronic properties of the multiferroic Ba₃NbFe₃Si₂O₁₄ were investigated by several methods, including synchrotron X-ray diffraction, Raman spectroscopy and synchrotron Mössbauer source technique at high quasi-hydrostatic pressures (up to 70 GPa), created in diamond anvil cells. At room temperature, two structural transitions at pressures of about 3.0 and 17.5 GPa were detected. Mössbauer studies at high pressures revealed a radical change in the magnetic properties during structural transitions. At pressures above 18 GPa, the crystal transforms into two magnetic fractions, and in one of them the Néel temperature (T_N) increases by about four times compared with the T_N value in the initial phase (from 27 to 115 K). At pressures above 50 GPa, a spin crossover occurs when the fraction of iron Fe³⁺ ions in oxygen octahedra transits from the high-spin (HS, S = 5/2) to the low-spin (LS, S = 1/2) state. This leads to a new change in the magnetic properties. The magnetic ordering temperature of the LS sublattice was found to be of about 22(1) K, and magnetic correlations between HS and LS sublattices were studied. Full article

(This article belongs to the Special Issue Spin Crossover (SCO) Research 2020)

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11 pages, 3868 KiB

Open AccessArticle

A Hidden Coordination-Bond Torsional Deformation as a Sign of Possible Spin Transition in Nickel(II)-Bis(nitroxide) Compounds

by Yukiya Kyoden and Takayuki Ishida

Molecules 2020, 25(17), 3790; https://doi.org/10.3390/molecules25173790 - 20 Aug 2020

Cited by 4 | Viewed by 1955

Abstract

Complex formation of nickel(II) tetrafluoroborate and tert-butyl 5-phenyl-2-pyridyl nitroxide (phpyNO) in the presence of sodium cyanate gave a discrete molecule [Ni(phpyNO)₂(X)₂] (X = NCO). The Ni-O-N-C_sp2 torsion angles were reduced on heating; 33.5(5)° and 36.2(4)° at 100 K vs. 25.7(10)° and 32.3(11)° at 400 K. The magnetic behavior was almost diamagnetic below ca. 100 K, and the χ_mT value reached 1.04 cm³ K mol⁻¹ at 400 K. An analysis using the van’t Hoff equation indicates a possible spin transition at T_1/2 >> 400 K. Density functional theory calculation shows that the singlet-quintet energy gap decreases as the structural change from 100 to 400 K. The geometry optimization results suggest that the diamagnetic state has the Ni-O-N-C_sp2 torsion angles of 32.7° while the S_total = 2 state has those of 11.9°. The latter could not be experimentally observed even at 400 K. After overviewing the results on the known X = Br, Cl, and NCS derivatives, the magnetic behavior is described in a common phase diagram. The Br and Cl compounds undergo the energy level crossing of the high-/low-spin states, but the NCS and NCO compounds do not in a conventional experimental temperature range. The spin transition mechanism in this series involves the exchange coupling switch between ferro- and antiferromagnetic interactions, corresponding to the high- and low-spin phases, respectively. Full article

(This article belongs to the Special Issue Spin Crossover (SCO) Research 2020)

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10 pages, 1706 KiB

Open AccessArticle

Influence of Molecular Orbitals on Magnetic Properties of FeO₂H_x

by Alexey O. Shorikov, Sergey L. Skornyakov, Vladimir I. Anisimov, Sergey V. Streltsov and Alexander I. Poteryaev

Molecules 2020, 25(9), 2211; https://doi.org/10.3390/molecules25092211 - 8 May 2020

Cited by 4 | Viewed by 2223

Abstract

Recent discoveries of various novel iron oxides and hydrides, which become stable at very high pressure and temperature, are extremely important for geoscience. In this paper, we report the results of an investigation on the electronic structure and magnetic properties of the hydride [...] Read more.

_{2}

_{x}

, using density functional theory plus dynamical mean-field theory (DFT+DMFT) calculations. An increase in the hydrogen concentration resulted in the destruction of dimeric oxygen pairs and, hence, a specific band structure of FeO

_{2}

with strongly hybridized Fe-

t_{2 g}

-O-

p_{z}

anti-bonding molecular orbitals, which led to a metallic state with the Fe ions at nearly 3+. Increasing the H concentration resulted in effective mass enhancement growth which indicated an increase in the magnetic moment localization. The calculated static momentum-resolved spin susceptibility demonstrated that an incommensurate antiferromagnetic (AFM) order was expected for FeO

_{2}

, whereas strong ferromagnetic (FM) fluctuations were observed for FeO

_{2}

H. Full article

(This article belongs to the Special Issue Spin Crossover (SCO) Research 2020)

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16 pages, 3047 KiB

Open AccessFeature PaperArticle

Effect of Multiplicity Fluctuation in Cobalt Ions on Crystal Structure, Magnetic and Electrical Properties of NdCoO₃ and SmCoO₃

by Vyacheslav A. Dudnikov, Yuri S. Orlov, Leonid A. Solovyov, Sergey N. Vereshchagin, Sergey Yu. Gavrilkin, Alexey Yu. Tsvetkov, Dmitriy A. Velikanov, Michael V. Gorev, Sergey V. Novikov and Sergey G. Ovchinnikov

Molecules 2020, 25(6), 1301; https://doi.org/10.3390/molecules25061301 - 12 Mar 2020

Cited by 7 | Viewed by 2875

Abstract

The structural, magnetic, electrical, and dilatation properties of the rare-earth NdCoO₃ and SmCoO₃ cobaltites were investigated. Their comparative analysis was carried out and the effect of multiplicity fluctuations on physical properties of the studied cobaltites was considered. Correlations between the spin state change of cobalt ions and the temperature dependence anomalies of the lattice parameters, magnetic susceptibility, volume thermal expansion coefficient, and electrical resistance have been revealed. A comparison of the results with well-studied GdCoO₃ allows one to single out both the general tendencies inherent in all rare-earth cobaltites taking into account the lanthanide contraction and peculiar properties of the samples containing Nd and Sm. Full article

(This article belongs to the Special Issue Spin Crossover (SCO) Research 2020)

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10 pages, 2093 KiB

Open AccessArticle

Reduced-Dimensionality Quantum Dynamics Study of the ³Fe(CO)₄ + H₂ → ¹FeH₂(CO)₄ Spin-inversion Reaction

by Toshiyuki Takayanagi, Yuya Watabe and Takaaki Miyazaki

Molecules 2020, 25(4), 882; https://doi.org/10.3390/molecules25040882 - 17 Feb 2020

Cited by 5 | Viewed by 2815

Abstract

Many chemical reactions of transition metal compounds involve a change in spin state via spin inversion, which is induced by relativistic spin-orbit coupling. In this work, we theoretically study the efficiency of a typical spin-inversion reaction, ³Fe(CO)₄ + H₂ → ¹FeH₂(CO)₄. Structural and vibrational information on the spin-inversion point, obtained through the spin-coupled Hamiltonian approach, is used to construct three degree-of-freedom potential energy surfaces and to obtain singlet-triplet spin-orbit couplings. Using the developed spin-diabatic potential energy surfaces in reduced dimensions, we perform quantum nonadiabatic transition state wave packet calculations to obtain the cumulative reaction probability. The calculated cumulative reaction probability is found to be significantly larger than that estimated from the one-dimensional surface-hopping probability. This indicates the importance of both multidimensional and nuclear quantum effects in spin inversion for polyatomic chemical reaction systems. Full article

(This article belongs to the Special Issue Spin Crossover (SCO) Research 2020)

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