Nathalie Guihéry

Nathalie Guihéry
Paul Sabatier University - Toulouse III | UPS Toulouse · Laboratoire de Chimie et Physique Quantiques - UMR 5626 - LCPQ

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111
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Publications

Publications (111)
Article
The Dzyaloshinskii Moriya interaction is expected to be at the origin of interesting magnetic properties, such as multiferroicity, skyrmionic states and exotic spin orders. Despite this, its theoretical determination is far from being established, neither from the point of view of ab initio methodologies, nor from that of the extraction technique t...
Article
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Trinuclear systems of formula [{Cr(L N3O2Ph )(CN) 2 } 2 M(H 2 L N3O2R )] (M = Mn II and Fe II , L N3O2R2 stands for pentadentate ligands) were prepared in order to assess the influence of the bending of the apical M‐N≡C linkages on the magnetic anisotropy of the Fe II derivatives and in turn on their SMM behaviors. The cyanido‐bridged [Cr 2 M] deri...
Article
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This article analyzes the electronic factors governing bond length alternation (BLA) in linear polyenes. The impact of the various effects is illustrated on small all-trans polyenes, namely butadiene, hexatriene and octatetraene prototype molecules. It is well known that self-consistent-field single determinant treatments overestimate the bond leng...
Article
This paper is a theoretical “proof of concept” on how the on-site first-order spin–orbit coupling (SOC) can generate giant Dzyaloshinskii–Moriya interactions in binuclear transition metal complexes. This effective interaction plays a key role in strongly correlated materials, skyrmions, multiferroics, and molecular magnets of promising use in quant...
Preprint
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We report the existence of a sizeable quantum tunnelling splitting between the two lowest electronic spin levels of mononuclear Ni complexes. The level anti-crossing, or magnetic clock transition, associated with this gap has been directly monitored by heat capacity experiments. The comparison of these results with those obtained for a Co derivativ...
Article
We report the existence of a sizeable quantum tunnelling splitting between the two lowest electronic spin levels of mononuclear Ni complexes. The level anti-crossing, or magnetic “clock transition”, associated with...
Article
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The magnetic anisotropy parameters of a hexacoordinate trigonally elongated Ni(II) complex with symmetry close to D3d are measured using field-dependent magnetization and High-Field and High-Frequency EPR spectroscopy (D = + 2.95 cm−1, |E/D| = 0.08 from EPR). Wave function based theoretical calculations reproduce fairly well the EPR experimental da...
Article
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We report the preparation and the full characterization of a novel mononuclear trigonal bipyramidal Co II complex [Co(NS 3 iPr )Br](BPh 4 ) ( 1 ) with the tetradentate sulphur containing ligand NS 3 iPr (N(CH 2 CH 2 SCH(CH 3 ) 2 ) 3 ). The comparison of its magnetic behaviour with those of two previously reported compounds [Co(NS 3 iPr )Cl](BPh 4 )...
Article
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A cyano-bridged Fe(II)−Cr(III) single-chain magnet designed to ensure a parallel orientation of the axial anisotropy of the building units is reported. This ferromagnetic chain compound consists of a pentagonal bipyramid Fe(II) complex with Ising-type anisotropy and a dicyanide Cr(III) complex interlinked through their apical positions. It is chara...
Article
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The magnetic anisotropy of a series of mononuclear complexes where the central metal ions varies from iron(II) to nickel(II) was thoroughly studied by combining complementary experimental techniques and theoretical calculations. Most originally, the zero-field-splitting parameters of the cobalt(II) derivatives were investigated by IR magnetospectro...
Article
The magnitude of the parameters of the various proposed model Hamiltonians used to model the macroscopic properties of the NiGa2S4 material and to interpret experimental observations is subject to controversy for more than a decade. Both the nature of the relevant operators (magnetic couplings, biquadratic exchange, anisotropic terms) and the value...
Article
Analytical expression of the interactions present in the Heisenberg Dirac van Vleck and Hubbard Hamiltonians have been derived as functions of both the energy of several broken symmetry DFT solutions and their expectation value of the S^2 spin operator. Then, following a strategy of decomposition of the magnetic exchange coupling into its main cont...
Chapter
Zero-field splitting (ZFS) is one of the essential ingredients for the occurrence of magnetic bistability at a molecular level. It is commonly understood as the loss of degeneracy of the spin components of a spin-orbit free electronic state in the absence of an external magnetic field. The loss of degeneracy finds its origin in the combined action...
Article
The preparation of a tetranuclear Ni(II) complex, made of two binuclear species bridged by a nitrate anion, using a macrocyclic cryptand like ligand is reported. The metal ions within the binuclear species are hexacoordinate with different distorted environments. One nickel site, Ni1, has as a compressed octahedral geometry, while the other nickel...
Article
The preparation of a binuclear Ni(II) complex with a pentacoordinate environment using a cryptand organic ligand and the imidazolate bridge is reported. The coordination sphere is close to trigonal bipyramidal (tbp) for one Ni(II) and to square pyramidal (spy) for the other. The use of the imidazolate bridge that undergoes π-π stacking with two ben...
Article
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Pentagonal bipyramid Fe(II) complexes have been investigated in order to evaluate their potential as Ising-spin building units for the preparation of hetero-polynuclear complexes that are likely to behave as SMMs. The considered monometallic complexes result from association of a divalent metal ion with pentadentate ligands having 2,6-diacetylpyrid...
Article
This paper describes the correlation between Ising-type magnetic anisotropy and structure in trigonal bipyramidal Co(II) complexes. Three sulfur-containing trigonal bipyramidal Co(II) complexes were synthesized and characterized. It was shown that we can engineer the magnitude of the Ising anisotropy using ligand field theory arguments in conjuncti...
Article
Full-text available
A challenge in molecular spintronics is to control the magnetic coupling between magnetic molecules and magnetic electrodes to build efficient devices. Here we show that the nature of the magnetic ion of anchored metal complexes highly impacts the exchange coupling of the molecules with magnetic substrates. Surface anchoring alters the magnetic ani...
Data
Supplementary Figures 1-19, Supplementary Tables 1-5, Supplementary Discussion and Supplementary References.
Article
The magnetic properties of the pentacoordinated [MII(Me4cyclam)N3]+ (Me4cyclam = tetramethylcyclam; N3 = azido and M = Ni and Co) complexes were investigated. Magnetization and EPR studies indicate that they possess an easy plane of magnetization with the axial anisotropy parameters D being close to 22 and larger than 30 cm-1 for the Ni and Co deri...
Article
Full-text available
A family of four-coordinate Fe(II) complexes formed with N,N'-chelating amido-pyridine ligands was synthesized, and their magnetic properties were investigated. These distorted tetrahedral complexes exhibit significant magnetic anisotropy with zero-field splitting parameter D ranging between -17 and -12 cm(-1). Ab initio calculations enabled identi...
Article
By using complementary experimental techniques and first-principles theoretical calculations, magnetic anisotropy in a series of five hexacoordinated nickel(II) complexes possessing a symmetry close to C2v , has been investigated. Four complexes have the general formula [Ni(bpy)X2 ](n+) (bpy=2,2'-bipyridine; X2 =bpy (1), (NCS(-) )2 (2), C2 O4(2-) (...
Article
Full-text available
This work addresses the question of the identification of the excited states that are mainly responsible for the magnitude and nature of the magnetic anisotropy in high-spin mononuclear transition metal complexes. Only few states are actually responsible for the single ion magnetic anisotropy, and these states can be anticipated from rather simple...
Chapter
The present chapter shows first that the topological Hückel Hamiltonian provides an analytical expression of both the singly occupied Molecular Orbitals and the spin density distribution of mono- and poly-radical conjugated hydrocarbons. It permits a new derivation of the Ovchinnikov’s rule (first established from a magnetic model Hamiltonian), whi...
Article
This article addresses the question of the possibility of obtaining high-spin chains and crowns of magnetic units s = 1 from doped (by a hole) antiferromagnetic architectures. It aims at determining the range of values of the double-exchange model interactions for which these molecules exhibit a high-spin ground state. Several chains and crowns of...
Article
Full-text available
This paper demonstrates the engineering and tuning of Ising-type magnetic anisotropy in trigonal bipyramidal Co(ii) complexes. Here, we predict that employing a ligand that forces a trigonal bipyramidal arrangement and has weak equatorial σ-donating atoms, increases (in absolute value) the negative zero field splitting parameter D. With these consi...
Article
Magnetic anisotropy is responsible for the single molecule magnet behavior of transition metal complexes. This behavior is characterized by a slow relaxation of the magnetization for low enough temperatures, and thus for a possible blocking of the magnetization. This bistable behavior can lead to possible technological applications in the domain of...
Article
This work re-examines the problem of the of broken-symmetry Density-Functional Theory (DFT) solutions in diradical systems, in particular for the calculation of magnetic couplings. The Ms=0 solution is not an eigenfunction of the S2 spin operator and the evaluation of the singlet state energy requires a spin-decontamination. A popular approximation...
Article
Herein we evaluate the influence of an electric field on the coupling of two delocalized electrons in the mixed-valence polyoxometalate (POM) [GeV14 O40 ](8-) (in short V14 ) by using both a t-J model Hamiltonian and DFT calculations. In absence of an electric field the compound is paramagnetic, because the two electrons are localized on different...
Article
Full-text available
The magnetic anisotropy of two pentacoordinate trigonal bipyramidal (C3v symmetry) Co(II) complexes [Co(Me6tren)Cl]ClO4 1 and [Co(Me6tren)Br]Br 2 was investigated and analysed by magnetic studies, high field multifrequency electron paramagnetic resonance (EPR) and ab initio calculations. Negative D parameters expressing an Ising type anisotropy (ea...
Article
A systematic study has been undertaken to determine how local distortions affect the overall (molecular) magnetic anisotropies in binuclear complexes. For this purpose we have applied a series of distortions to two binuclear Ni(II) model complexes and extracted the magnetic anisotropy parameters of multispin and giant-spin model Hamiltonians. Furth...
Article
This work compares three descriptions of the unpaired electrons distribution in conjugated mono-radical and di-radical hydrocarbons involving one or two methylene groups attached to an aromatic skeleton. The first one is the simple Hückel topological Hamiltonian, the singly occupied molecular orbitals (SOMO) of which may be analytically obtained. T...
Article
The objective of this paper is to design a consistent series of organic molecules that may present a double exchange mechanism and study their low energy spectrum using spin unrestricted Density Functional Theory. For this purpose, organic tetra-methylene methane units having an S = 1 spin ground state and diamagnetic organic bridges are taken as b...
Article
The use of accurate model Hamiltonians is crucial to extract information on the magnetic interactions from the raw data obtained from magnetic susceptibility measurements, EPR, or NMR spectroscopy. Combining information from different experimental techniques can be used to propose topologies and magnitudes of the magnetic couplings in the system. I...
Article
The determination of anisotropic magnetic parameters is a task of both experimental and theoretical interest. The added value of theoretical calculations can be crucial for analyzing experimental data by (i) allowing assessment of the validity of the phenomenological spin Hamiltonians, (ii) allowing discussion of the values of parameters extracted...
Article
The procedure to extract and identify from broken-symmetry density functional theory (BS-DFT) calculations the various components of the magnetic couplings in diradicals [J. Chem. Phys. 2012, 137, 114106] is re-examined. It is shown that this previous decomposition scheme fails for systems exhibiting large core polarization effects and hence become...
Article
This paper reports the experimental and theoretical investigations of two trigonal bipyramidal Ni(II) complexes, the [Ni(Me6tren)Cl](ClO4) 1 and [Ni(Me6tren)Br](Br) 2. High Field, High frequency Electron Paramagnetic Resonance spectroscopy performed on a single crystal of the [Ni(Me6tren)Cl](ClO4) 1 shows a giant uniaxial magnetic anisotropy with a...
Article
In spin-crossover (SCO) compounds exhibiting a light induced excited spin state trapping (LIESST) effect, the thermodynamic T(1∕2) and kinetic T(LIESST) temperature values depend on the features of the potential energy surfaces (PES) of the two lowest singlet and quintet states but also on vibrational contributions, collective effects, such as elec...
Article
The nature and magnitude of the magnetic anisotropy of heptacoordinate mononuclear Ni(II) and Co(II) complexes were investigated by a combination of experiment and ab initio calculations. The zero-field splitting (ZFS) parameters D of [Ni(H(2) DAPBH)(H(2) O)(2) ](NO(3) )(2) ⋅2 H(2) O (1) and [Co(H(2) DAPBH)(H(2) O)(NO(3) )](NO(3) ) [2; H(2) DAPBH=2...
Article
This work addresses the following paradox observed in diradicalar conjugated hydrocarbons: while the natural orbitals occupation numbers clearly indicate only two open-shell orbitals, i.e. two unpaired electrons, the minimal CAS zero-order description fails to reproduce accurately the electronic structures of the lowest states (spin density distrib...
Article
We present a new and simple scheme that aims to decompose into its main physical contributions the magnetic exchange interaction between two unpaired electrons. It is based on the popular broken-symmetry density functional theory (DFT) approach and relies on the frozen orbital capabilities of the local self-consistent field method. Accordingly, the...
Article
The electrical conductivities and plausible charge-ordering states in the room temperature (r.t.) phase for MMX chains [Ni(2)(dta)(4)I](∞) and [Pt(2)(dta)(4)I](∞) (dta = CH(3)CS(2)(-)) have been analyzed with periodic density functional theory (DFT) and correlated ab initio calculations combined with the effective Hamiltonian theory. Periodic DFT c...
Article
Cupric oxide (CuO) has been described as belonging to the quasi-one-dimensional antiferromagnetic compounds. It has also been suggested that cupric oxide possesses strong magnetic anisotropy, which is possibly related to the observed ferroelectricity in this material. In this paper, the magnetic interactions of CuO are investigated using the embedd...
Article
This work addresses the conception of purely organic magnetic materials by properly bridging high-spin polycyclic hydrocarbons A and B, through covalent ligands L. The strategy varies two degrees of freedom that govern the magnetic character of the A-L--B sequence, namely, the bridge response to spin polarization and the relative signs of spin dens...
Article
Pentagonal-bipyramidal complexes [Co(DABPH)X(H(2)O)]X [X = NO(3) (1), Br (2), I (3)] were synthesized, and their magnetic behavior was investigated. Simulation of the magnetization versus temperature data revealed the complexes to be highly anisotropic (D ≈ +30 cm(-1)) and the magnitude of the anisotropy to be independent of the nature of the axial...
Article
The physical factors governing the magnetic coupling between two magnetic sites are analyzed and quantified as functions of the length of the bridging conjugated ligand. Using wave-function-theory based ab initio calculations, it has been possible to separate and calculate the various contributions to the magnetic coupling, i.e. the direct exchange...
Article
The zero-field splitting of the copper acetate monohydrate complex is studied using wave function based calculations. The anisotropy parameters extracted from highly correlated methods are in excellent agreement with the most accurate experimental results; in particular, the negative sign of the axial anisotropy parameter D is reproduced. During se...
Article
The antisymmetric magnetic interaction is studied using correlated wave-functionbased calculations in oxo-bridged copper bimetallic complexes. All of the anisotropic multispin Hamiltonian parameters are extracted using spin-orbit state interaction and effective Hamiltonian theory. It is shown that the methodology is accurate enough to calculate the...
Article
The zero-field splitting (ZFS) of a model monometallic Mn(III) complex is theoretically studied as function of a systematic symmetry lowering. First, we treat the octahedral case for which the standard S.D.S model Hamiltonian cannot be applied due to a zero-field splitting in the absence of anisotropy induced by the spin-orbit coupling between the...
Article
This paper studies the physical basis of the giant-spin Hamiltonian, which is usually used to describe the anisotropy of single-molecule magnets. A rigorous extraction of the model has been performed in the weakexchange limit of a binuclear centrosymmetric Ni�II� complex, using correlated ab initio calculations and effective Hamiltonian theory. It...
Article
DFT calculations are performed on a model mixed-valence system presenting a double exchange phenomenon. Due to the intrinsic multireference character of the lowest Ms components of the spin states, it is shown that the interactions involved in the double-exchange model cannot be simply extracted from the DFT energies as it is sometimes done. It is,...
Article
The magnetic anisotropy of the [Ni2(en)4Cl2]2+ (en ) ethylenediamine) complex has been studied using wave function based computational schemes. The spin-orbit state interaction methodology provides accurate ab initio energies and wave functions that are used to interpret the anisotropy in bimetallic complexes. The extraction of the anisotropic spin...
Article
Monometallic Ni(II) and Co(II) complexes with large magnetic anisotropy are studied using correlated wave function based ab initio calculations. Based on the effective Hamiltonian theory, we propose a scheme to extract both the parameters of the zero-field splitting (ZFS) tensor and the magnetic anisotropy axes. Contrarily to the usual theoretical...
Article
The aim of the work is to give an explanation of the magnetic properties of a mixed-valence [GeV14O40]8– polyoxometalate reduced by two electrons, which, in contrast to what happens in other two-electron-reduced polyoxometalates, does not show any magnetic coupling between the two unpaired electrons. For this purpose, a quantitative evaluation of t...
Article
This paper provides a qualitative analysis of the physical content of the low-energy states of a spin-transition compound presenting a light-induced excited spin state trapping (LIESST) phenomenon, namely, [Fe(dipyrazolpyridine)2](BF4)2, which has been studied using the wave function-based CASPT2 method. Both the nature of the low-energy states and...
Article
The variational energies of broken-symmetry single determinants are frequently used (especially in the Kohn-Sham density functional theory) to determine the magnetic coupling between open-shell metal ions in molecular complexes or periodic lattices. Most applications extract the information from the solutions of m(s)(max) and m(s)(min) eigenvalues...
Article
Two noninnocent ligands are theoretically studied using wave function based methods to demonstrate their ability to undergo singlet-triplet transition under the effect of an external charge mimicking the electrostatic role of a metal ion. It is shown that the singlet-triplet energy difference is very sensitive to the metal ion charge which tunes th...
Article
This paper analyzes the different contributions to the magnetic coupling in systems with more than one unpaired electron per center. While in S=12 spin systems the Heisenberg Hamiltonian involving only bilinear exchange interactions is reliable for the description of the magnetic states, biquadratic exchange interactions must be sometimes introduce...
Article
We have reanalyzed the microscopic origin of the isotropic deviations that are observed from the energy spacings predicted by the Heisenberg–Dirac–van Vleck (HDVV) Hamiltonian. Usually, a biquadratic spin operator is added to the HDVV Hamiltonian to account for such deviations. It is shown here that this operator cannot describe the effect of the e...
Article
Full-text available
The leading electronic interactions governing the local physics of the CE phase of half-doped manganites are extracted from correlated ab initio calculations performed on an embedded cluster. The electronic structure of the low-energy states is dominated by double exchange configurations and O-2$p_{\sigma}$ to Mn-3d charge transfer configurations....
Chapter
Ab initio calculations combined with the effective Hamiltonian theory of Bloch provide a rational way to determine model Hamiltonians. The embedded cluster approach is the most reliable method of extraction of effective interactions for the study of highly correlated material. In the specific case of half-doped man-ganites, several model Hamiltonia...
Article
Properties in manganites are often interpreted in terms of double exchange mechanism. A dimer of manganese sites bearing a hole is seen as a mixed valence entity ruled by a double exchange Hamiltonian. They can, however, be considered as ferrimagnetic local units if the holes are localized on the bridging oxygen atoms as implicitly suggested by rec...
Article
This paper first comments on the surprisingly poor status that Quantum Chemistry has offered to the fantastic intuition of Lewis concerning the distribution of the electrons in the molecule. Then, it advocates in favor of a hierarchical description of the molecular wave-function, distinguishing the physics taking place in the valence space (in the...
Article
A truncated Hubbard model is developed for the description of the electronic structure of odd-electron TM-L-TM units (TM=transition metal and L=ligand). The model variationally treats both the double exchange and purely magnetic Heisenberg configurations. This Hubbard model can either be mapped on a purely magnetic Heisenber model in which the brid...