La synthèse supramoléculaire permet de dépasser le jeu du hasard dans les rencontres intermoléculaires en programmant l’assemblage des briques moléculaires selon des stratégies déterministes. De telle prédispositions architecturales sont d’un intérêt majeur en nanosciences pour l’obtention de nano-objets moléculaires et leur organisation à l'échelle nanométrique.On peut imaginer réaliser des dispositifs de taille nanométrique en dotant de propriétés particulières les synthons de ces assemblages. Le travail présenté dans cette thèse de doctorat illustre en intégralité cette démarche, de la synthèse à la caractérisation des propriétés magnétiques de baguettes dinucléaires et grilles tétranucléaires dont les sites métalliques sont paramagnétiques. Une étude approfondie des conditions d’obtention de ces objets a été effectuée en utilisant des méthodes de caractérisation physico-chimiques. L’étude de leurs propriétés magnétiques a été menée principalement par Résonance Paramagnétique Électronique pour étudier les complexes formés en solution. Les contraintes géométriques qui sont exploitées par la synthèse supramoléculaire présentent un intérêt pour l’obtention de propriétés magnétiques particulières. / The elaboration of well-defined geometrical molecular arrangements is a key issue of supramolecular chemical synthesis. This ability is of major interest in the field of nanosciences in order to get well organized supramolecular architectures at the nanoscale. Upon endowing with peculiar physical and/or chemical properties the molecular synthons of such architectures one may think of building original devices. Such a strategy is actually the driving force of this PhD work, which reports on the synthesis and the subsequent characterization of dinuclear stick and tetranuclear grid complexes with paramagnetic metal ions. A comprehensive study of the stability in solution of these supramolecular objects has been carried out with the help of various spectroscopic methods. A thorough investigation of their magnetic properties has been performed in solution by Electron Paramagnetic Resonance spectroscopy. Thanks to its geometrical rules, the efficiency of the supramolecular synthetic strategy is demonstrated to determine the magnetic properties of the studied complexes.

In order for molecular magnetic materials to become applicable, they must retain their magnetisation at reasonable temperatures, which can be achieved with high energy barriers for spin reversal and high blocking temperatures. In the field of Single-Molecule Magnets (SMMs), over the last decade, the main focus has shifted from large spin complexes to highly anisotropic systems which have displayed record energy barriers. There are two main methods of increasing magnetic anisotropy in a complex: i) Choosing a metal ion that boasts high magnetic anisotropy then coupling two such ions through magnetic interactions to induce large global anisotropy, and ii) maintain a low spin or use a mononuclear complex while minimising quantum tunnelling of the magnetisation by controlling the geometric features of the metal ion. Both strategies are equally valid and have been explored in this thesis using dinuclear lanthanide as well as mononuclear 3d complexes. In the pursuit of high-barrier SMMs via alignment of anisotropy axes, two dinuclear, quadruple-stranded helicates and one mesocate were isolated and are described in detail herein, both structurally and magnetically. Furthermore, theoretical calculations have been performed to determine the energies of Kramers doublets on each DyIII centre to derive magneto-structural correlations. To induce magnetic interactions between DyIII ions, a centrosymmetric dinuclear SMM was synthesised. Investigation of the crucial DyIII…DyIII interaction as well as its effect on the quantum tunnelling of the magnetisation has been carried out using ab initio calculations and magnetic dilution studies. Using the same system, a method of greatly enhancing the energy barriers in SMMs has been developed. It involves modifying the coordinating ligands to include electron withdrawing groups in order to yield more anisotropic metal ions. The energy barrier for spin reversal has been increased 7-fold in one case. While lanthanide chemistry has proven to be quite versatile and promising, a new branch of nanomagnets is currently being pursued: mononuclear 3d complexes as SMMs. The advantages of 3d metals include high anisotropy per ion, low spin (as anisotropy decreases with increasing spin), well-understood electronic structures and clear correlations between geometry and magnetic anisotropy. The structural and magnetic properties of three complexes based on CoII and terpyridine ligands as well as a seven-coordinate CoII complex with positive anisotropy are discussed at length. The unique slow relaxation dynamics and spin crossover behaviour has been followed using DFT and ab initio calculations, as well as EPR and magnetic dilution studies. Overall, this thesis describes the efforts taken to synthesise high-barrier nanomagnets through understanding the origins and mechanisms of slow magnetic relaxation in both lanthanide and 3d metal complexes.

A collection of studies are reported that focus on the examination of exchange interactions in complexes containing paramagnetic ions with a large magnetic anisotropy. A number of complementary techniques are used to analyse the complicated systems that arise, including high-field high-frequency electron paramagnetic resonance, inelastic neutron scattering, SQUID magnetometry, and ab initio calculations. The nuclearity of the complexes ranges from dimetallic, to trimetallic, to octametallic. A family of five water- and carboxylate-bridged nickel(II) dimetallics are the focus of a magneto-structural correlation study that succeeds in measuring the magnitude of the exchange interaction despite dominating effects from large zero-field splitting effects. Similar work is reported for four cobalt(II) analogues of these compounds, with the relationship between exchange interactions and geometry also being probed by pressure INS. Charge density studies that combine high resolution X-ray and neutron diffraction studies are reported on cobalt and nickel analogues from the same family of dimetallics, revealing strong evidence for non-direct exchange. A family of four trimetallic triangle complexes containing two nickel(II) ions and one chromium(III) ion bridged by a central fluoride and a total of six carboxylates are reported, and the exchange interactions are elucidated from a global model that accounts for the low-field magnetic, heat capacity, and EPR data. Two new octametallic vanadium(III) wheels—where each pair of adjacent metals are bridged by a fluoride and two carboxylates—are reported along with preliminary results from magnetic measurements and solid state proton NMR spectra, which reveal significant field-dependent effects arising from level crossings at high fields.

Molecular Nanomagnets have been proposed as plausible candidates in a variety of futuristic applications. Thorough understanding of the magnetic properties of these systems is therefore necessary to develop devices that include such units. The aim of this thesis is to synthesise and structurally and magnetically characterise a range of systems that could be used as elementary units in three proposed applications such as: data storage devices, magnetic refrigerants and qubits for quantum computing. A series of mixed 3d/4f metal complexes were synthesised through solvothermal reactions and characterised by X-ray single crystal diffraction and SQUID magnetometry. Through indirect methods it was possible to obtain high magnetic entropy change for some systems. It was also possible to obtain some insight into the magnetic interactions within the systems through modelling the magnetic data. The role of the 4f-4f and 3d-4f interactions in two sets of molecules is also described. The first study is in an asymmetric dysprosium dimer, where through a range of experimental techniques and advanced theoretical methods, such ab-initio calculations we are able to explain the role of the intramolecular interactions and their effect on the SMM properties of this system. Similarly, insight into the role of the 3d-4f interactions is achieved through the observation of the magnetic behaviour of a family of 27 tetranuclear systems, though SQUID data and ab-initio calculations. Finally, chemical functionalization of a well-proposed qubits, namely {Cr7Ni} and subsequent reaction with a redox active metal ion, CoII/III, two {Cr7Ni} systems are linked. The magnitude of the exchange interaction between the {Cr7Ni}-CoII-{Cr7Ni} was determined through Electron Paramagnetic Resonance. Furthermore, by chemical oxidation/reduction of the cobalt between paramagnetic and diamagneticstates, i.e. CoII and CoIII respectively, we demonstrate that the interaction can be switched ON/OFF. This characteristic makes of these systems candidates to function as a SWAP gate.

Les molécules-aimants sont des complexes moléculaires contenant des ions des métaux de transition ou des lanthanides capables de présenter le phénomène de blocage de l’aimantation en dessous d’une température de blocage Tb. Ce blocage est dû à la présence d’une barrière d’énergie de réorientation de leur aimantation à cause de la présence d’une anisotropie magnétique uniaxiale qui conduit à la présence de deux états stables de l’aimantation.Ces deux états stables sont adressables avec un champ magnétique extérieur. Il est donc,théoriquement, envisageable d’utiliser ces molécules comme unités de base pour le stockage « classique » de l’information.Néanmoins, à cause de la nature quantique des molécules, une relaxation entre les deux états de l’aimantation a lieu à basse température par effet tunnel à travers la barrière d’énergie. Cet effet tunnel a plusieurs causes dont une correspondant à une légère déviation de l’anisotropie magnétique de la situation strictement axiale. Cet effet annule le caractère bistable (classique) des molécules les rendant inutilisables comme bits classiques pour le stockage de l’information. Mais, la présence de l’effet tunnel conduit à une situation particulière à basse température où deux niveaux sont présents séparés par une énergie liée au caractère non axiale (rhombique) de l’aimantation (cas où le spin est entier). Un système à deux niveaux est appelé bit quantique(qubit) et constitue l’unité de base pour la construction d’ordinateurs quantiques si plusieurs conditions sont réunies.Ainsi, pour concevoir des bits classiques ou quantiques, il est indispensable comprendre au niveau microscopique la nature de l’anisotropie magnétique et les facteurs qui l’influencent.Ce travail de thèse est consacré à l’étude théorique de la nature de l’anisotropie magnétique dans des complexes mononucléaires et binucléaires de Ni(II) (S = 1)et de Co(II) (S = 3/2). Des calculs de type ab initio, basés sur la théorie de la fonction d’onde,qui permettent d’extraire les paramètres de l’hamiltonien de spin de l’anisotropie magnétique ont été effectués. Des calculs sur des objets modèles et molécules réelles qui permettent de séparer l’effet des différents paramètres structuraux et électroniques des ligands sur la nature et l’amplitude de l’anisotropie magnétique ont aussi été réalisés.La comparaison entre les calculs sur des complexes modèles et sur des complexes réels permet de rationaliser les propriétés magnétiques des complexes réels et surtout de proposer des stratégies pour la synthèse de nouveaux complexes avec les propriétés souhaitées. L’étude de complexes binucléaires qui peuvent être considérés comme la première étape pour la conception de porte logique quantique a été réalisée. Les calculs sur les complexes binucléaires sont réalisés en fragmentant les molécules en deux espèces mononucléaires. Pour les complexes binucléaires de Ni(II) et Co(II), des calculs de type Density Functional Theory (DFT) pour évaluer l’amplitude et la nature de l’interaction d’échange ont été menés. Pour étudier l’influence d’une perturbation extérieure sur les propriétés magnétiques, l’influence d’un champ électrique placé parallèle et perpendiculaire à l’axe de facile aimantation d’un complexe de Ni(II) a été étudiée. Le champ électrique peut influencer les propriétés d’anisotropie de manière importante ouvrant la possibilité à la manipulation des molécules par cette perturbation. / Single molecule magnets are molecular complexes containing transition metal or lanthanides ions which are able to block their magnetization below a certain blocking temperature Tb. This blocking is caused by an energy barrier separating the two orientations of magnetization leading to two stable magnetization states. These two states can be controlled by an external magnetic field.Therefore, it is theoretically possible to use these molecules as bits which are able to store“classical” information. However, due to the quantum nature of these molecules, the relaxation of magnetization can exist even at low temperatures. This phenomenon is called the quantum tunneling effect and prevents the bistable (classical) behavior of the magnetic properties, as well as their use as classical bits for data strorage.Yet, the quantum tunneling of the magnetization also leads to a particular situation at a low temperature where two levels are separated by an energy related to the non-axial character(rhombic) of the magnetization (when the spinis an integer). Such two-levels system could be used as a quantum bit (qbit) which is the basic unit for quantum information processing. Thus,the design of classical or quantum bits require a precise understanding of magnetic properties and their origin at a microscopic level.The Ph.D work was devoted to the theoretical study of the magnetic anisotropy in mononuclear and binuclear Ni(II) (S=1) and Co(II) (S=3/2) complexes. Ab initio calculations based on the wave function theory were carried out and the spin Hamiltonian parameters were extracted. Model complexes were used to investigate the structural and electronic parameters causing magnetic anisotropy.Calculations were, also, performed on complexes synthesized in the laboratory.Comparison between real and model complexes allowed rationalizing the magnetic properties and imagining new synthesis strategies leading to the desired magnetic properties. Binuclear complexes that can be considered as double qbits and used to build quantum logic gates were also investigated. The calculations were performed by fragmenting the binuclear complexes into two mononuclear units in order to study the local anisotropy of each metal ion.The exchange interaction was investigated using Density Functional theory (DFT). In order to study the influence of an external perturbation on magnetic properties, the magnetic properties of a mononuclear Co(II) complex under an external electric field applied parallel or perpendicular to the axis of easy magnetization were calculated. The application of an electric field can lead to important modifications of magnetic properties. Thereby, offering the possibility to the manipulation of these molecules by external electric fields.

The controlled assembly of molecular building blocks is an emerging strategy that allows for the preparation of materials with tailor-made properties. This involves the precise combination of molecular subunits that interact with one another via specifically designed reactive sites. Such a strategy has produced materials exhibiting remarkable properties, including those based on metal-organic frameworks and single-molecule magnets. The present Thesis aims to highlight how such metal-organic assemblies can be engineered at the molecular level to promote certain desired functionalities. Specifically, Chapter 2 will focus on the confinement effects of a crystalline sponge on a ferrocene-based guest molecule that is nanostructured within the porous cavities of a host material. In doing so, we evaluate how one can exert some level of control over the binding sites of the guest molecule, through the addition of electron-withdrawing groups, as well as tuning the physical properties of the guest itself through molecular encapsulation. Notably, we demonstrate a distinct change in the dynamic rotational motion of the ferrocene molecules once confined within the crystalline sponge. In Chapter 3, we investigate the generation of slow relaxation of the magnetization from a Co(II)-based metal-organic framework. We compare this to a closely related 2D Co(II) sheet network, and how slight changes in the crystal field, probed through computational methods, can impact the magnetic behaviour. This type of study may be particularly beneficial in the optimization of single-ion magnets, by sequestering metal centres in select chemical environments, and minimizing molecular vibrations that may offer alternative magnetic relaxation pathways. We extend these principles in Chapter 4, through the use of a nitrogen-rich ligand that acts as a scaffold for Ln(III) ions, thereby yielding 0D and 1D architectures. The coordination chemistry of Ln(III) ions with N-donor ligands remains scarce, especially when evaluated from a magnetic perspective, and therefore, we sought to determine the magnetic behaviour of such compounds. The monomeric unit displays clear single-molecule magnet behaviour with an energetic barrier for the reversal of the magnetization, while the 1D chain displays weaker magnetic characteristics. Nevertheless, such compounds incorporating nitrogen-rich ligands offer much promise in the design of environmentally-friendly energetic materials. In Chapter 5, we take a look at different two different systems that involve the formation of radical species. On one hand, we can promote enhanced magnetic communication between Ln(III) ions, which is typically quite challenging to achieve given the buried nature of the 4f orbitals, and on the other hand, we rely on a redox-active ligand to design stimuli-responsive metal-organic assemblies. The latter case provides access to “smart” molecular materials that can respond to changes in their environment. Here, a multi-stimuli responsive nanobarrel was studied, which displayed sensitivity to ultraviolet radiation, heat and chemical reduction. Lastly, Chapter 6 provides a new method for the systematic generation of cationic frameworks, termed Asymmetric Ligand Exchange (ALE). This strategy focuses on the replacement of linear dicarboxylates with asymmetric linkers that features one less negative charge, in order to tune the ionicity of porous frameworks. This allows for the retention of the structural topology and chemical reactivity of the original framework, representing distinct advantages over other similar strategies. Methods to retain permanent porosity in such cationic frameworks are also proposed. Altogether, these studies highlight how the directed assembly of ordered networks can generate varied properties of high scientific interest.

Ce travail de thèse explorait certains aspects de la chimie de coordination de complexes moléculaires à bases de métaux 3d (Fe, Cu, Mn et Ni) supportés par des ligands azotés de type aroyle-hydrazone. Le travail de cette thèse était plus particulièrement centré sur le développement des nouveaux ligands et la photo chimie des complexes ferriques, afin d’élucider en particulier les mécanismes de la photo réduction qui valorise un brevet du laboratoire sur la production et le stockage d’énergie solaire via la photo réduction d’ions ferriques. Les complexes mis en jeu dans le processus ont été totalement caractérisés en solution et à l’état solide. Ce phénomène prend place en solution comme en solution gelée. La cinétique du processus photochimique a été suivie par UV-Visible comme par RPE. Cette photo réduction passe par un intermédiaire radicalaire et le solvant joue le rôle du donneur des électrons. Ce processus a été totalement étudié : l’effet du solvant, l’effet de la modification dans la sphère de coordination du complexe, l’effet de la modification de la périphérie des ligands et finalement l’effet des longueurs d’ondes. D’autres domaines sont également explorés, comme le magnétisme moléculaire ou encore la catalyse homogène (oligomérisation de l’éthylène) avec des complexes à base de Ni2+. / This PhD thesis explored some aspects of the coordination chemistry of molecular complexes based on 3d transition metal ions (Fe, Cu, Mn and Ni) coordinated by multidentate aroyl-hydrazone ligands. The work of this thesis was particularly focused on the development of new ligands, their coordination chemistry and the photochemistry of ferric complexes. The central objective of this work was to elucidate the mechanism of the photo reduction process, in order to valorize an already accepted laboratory patent on the production and storage of solar energy. The complexes involved in the process have been fully characterized in solution and in the solid state. This phenomenon takes place in solution as in frozen solution. The kinetics of the photochemical process was followed by UV-Visible as by RPE. This photo reduction passes through a radical intermediate and the solvent plays the role of the electron donor. This process has been fully studied: the effect of the solvent, the effect of the modification in the coordination sphere of the complex, the effect of the modification of the periphery of the ligands and finally the effect of the light and different wavelengths. Other fields are also explored, such as molecular magnetism for different mono and dinuclear iron and manganese complexes or even homogeneous catalysis (oligomerization of ethylene) with complexes based on Ni(II).

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La physique quantique appliquée à la théorie de l’information se révèle être pleine de promesses pour notre société. Conscients de ce potentiel, des groupes de scientifiques du monde entier ont pour objectif commun de créer un ordinateur utilisant les principes de la mécanique quantique. La premières étape de cet ambitieux cheminement menant à l’ordinateur quantique est la réalisation du bloc de base de l’encodage quantique de l’information, le qubit. Dans le large choix de qubits existants, ceux utilisant un spin sont très attrayants puisqu’ilspeuvent être lus et manipulés de façon cohérente uniquement en utilisant des champs électriques. Enfin, plus un système est isolé, plus son comportement demeure quantique, ce qui fait du spin nucléaire un sérieux candidat dans la course aux long temps de cohérence et donc aux grands nombres d’opérations quantiques.Dans ce contexte, j’ai étudié un transistor de spin moléculaire. Ce dispositif, placé dans un réfrigérateur à dilution assurant des mesures à 40mK, est composé d’une molécule magnétique TbPc2 couplée à des électrodes (source, drain et grille) et à une antenne hyperfréquence. Il nous a permis de lire à l’aide d’une mesure de conductance, à la fois l’état de spin électronique et nucléaire de l’ion Terbium. Ma thèse se focalise sur l’étude de la dynamique de ces spins et plus particulièrement celle du spin nucléaire 3/2 sous l’influence d’un champ micro-onde. La première étape consiste à mesurer la différence d’énergie entreces quatre états de spin nucléaire pour ensuite parvenir à manipuler de façon cohérente ses trois transitions en utilisant uniquement un champ électrique. Pour caractériser davantage les processus de décohérence à l’origine de la perte de phase des états quantique, j’ai réalisé des mesures Ramsey et Hahn-echo révélant des temps de cohérence de l’ordre de 0.3ms. Ces résultats préliminaires montrent que nous sommes en présence de 3 qubits ayant une figure de mérite supérieure à deux milles, répondant ainsi aux attentes suscitées par l’utilisation d’un spin nucléaire comme bloc de base de l’information quantique.Plus que démontrer expérimentalement la dynamique de trois qubits, ces mesures nous prouvent qu’un spin nucléaire intégré dans une géométrie de type transistor à aimant moléculaire est un système à quatre états contrôlé de façon cohérente. Des propositions théoriques démontrent qu’un traitement quantique de l’information, telle que l’application de portes quantiques et la réalisation d’algorithmes, peuvent être implémentées sur un tel système. Je me suis concentré sur un algorithme de recherche. Il s’agit de la succession d’une porteHadamard, qui crée une superposition cohérente de tous les états de spin nucléaire, et une évolution unitaire qui amplifie l’amplitude d’un état désiré. Il permet une accélération quadratique de la recherche d’un élément dans une liste non ordonnée comparée à un algorithme classique. Pendant ma thèse, j’ai apporté la preuve expérimentale de la faisabilité de cet algorithme de Grover sur un système à plusieurs niveaux. La première étape a été de créer une superposition cohérente de 2, 3 et 4 états par l’application d’un pulsation radio-fréquence. Enfin, j’ai mesuré une oscillation cohérente entre une superposition de trois états et un état sélectionné qui est la signature de l’implémentation de l’algorithme de recherche.En résumé, cette thèse expose la première implémentation d’un algorithme quantique de recherche sur un qudit de type aimant moléculaire. Ces résultats, combinés à la grande polyvalence des molécules magnétiques, sont autant de promesses pour la suite de ce défi scientifique qu’est la construction d’un ordinateur quantique moléculaire. / The application of quantum physics to the information theory turns out to be full of promises for our information society. Aware of this potential, groups of scientists all around the world have this common goal to create the quantum version of the computer. The first step of this ambitious project is the realization of the basic block that encodes the quantum information, the qubit. Among all existing qubits, spin based devices are very attractive since they reveal electrical read-out and coherent manipulation. Beyond this, the more isolated a system is, the longer its quantum behaviour remains, making of the nuclear spin a serious candidate for exhibiting long coherence time and consequently high numbers of quantum operation.In this context I worked on a molecular spin transistor consisting of a TbPc2 singlemolecule magnet coupled to electrodes (source, drain and gate) and a microwave antenna. This setup enabled us to read-out electrically both the electronic and the nuclear spin states and to coherently manipulate the nuclear spin of the Terbium ion. I focus during my Ph.D. on the study of the spins dynamic and mainly the 3/2 nuclear spin under the influence of a microwave pulse. The first step was to measure the energy difference between these statesleading in a second time to the coherent manipulation of the three nuclear spin transitions using only a microwave electric field. To further characterize the decoherence processes that break the phase of the nuclear spin states, I performed Ramsey and Hahn-echo measurements. These preliminary results show that we were in presence of three qubits with figure of merit higher than two thousands, thus meeting the expectations aroused by the use of a nuclearspin as the basic block of quantum information.More than demonstrating the qubit dynamic, I demonstrated that a nuclear spin embedded in the molecular magnet transistor is a four quantum states system that can be fully controlled, a qudit. Theoretical proposal demonstrated that quantum information processing such as quantum gates and algorithms could be implemented using a 3/2 spin. I focused on a research algorithm which is a succession of an Hadamard gate, that creates a coherent superposition of all the nuclear spin sates, and an unitary evolution, that amplified the amplitude of a desired state. It allows a quadratic speed-up to find an element in an unordered list compared to classical algorithm. During my Ph.D., I demonstrated the experimental proof of feasibility of this Grover like algorithm applied to a multi-levels system. The first step was to experimentally create coherent superposition of 2, 3 and 4 states. Then I measured coherent oscillations inbetween a 3 state superposition and a selected state which is the signature of the research algorithm implementation.In summary, this Ph.D. exposed the first quantum search algorithm on a single-molecule magnet based qudit. These results combined to the great versatility of molecular magnet holds a lot of promises for the next challenge: building up a scalable molecular based quantum computer.

La Théorie de la Fonctionnelle de la Densité (DFT) combinée avec la méthode de la Symétrie Brisée (BS) est aujourd'hui très utilisée dans le domaine du magnétisme moléculaire pour le calcul des constantes d'échange. Cette méthode (DFT-BS) reste cependant semi-quantitative et elle souffre de défauts déjà discutés dans la littérature. Dans le but de mieux en comprendre l'origine, nous avons réexaminé les contributions physiques qui participent au mécanisme d'échange. Nous proposons alors plusieurs formules analytiques construites suivant deux approches complémentaires (orbitales moléculaires et liaison de valence). Au cours de notre analyse, nous avons soulevé un problème inédit relatif à l'état de symétrie brisée tel que livré par le calcul DFT. Nos modèles seront appliqués au cas des dimères de cuivre(II) et nous verrons comment quantifier les différents paramètres afin de reconstruire les constantes d'échange. Qui plus est, notre travail permet d'établir une correspondance quantitative originale entre les deux approches pré-citées. / Density Functional Theory (DFT) combined with the Broken Symmetry (BS) method is today widely used in the field of molecular magnetism for the computation of exchange coupling constants. But this method (DFT-BS) remains semi-quantitative as it suffers from a series of drawbacks already discussed in the literature. In order to better understand the origin of such problems, we reexamined the physical contributions acting in the exchange phenomenon. We then propose alternative analytical expressions built along two complementary approaches (molecular orbitals and valence bond). During our analysis, we found a new problem linked to the broken symmetry state as it comes out of a DFT calculation. Our models will be applied to copper(II) dimers and we will show how to quantify the different parameters involved in order to reconstruct the coupling constants. Moreover, our work allows for an original quantitative correspondence between the two above-mentioned approaches.