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Síntesi de complexos de coordinació derivats de macrocicles nitrogenats. Estudi magnètic
No full textTreballs Finals de Grau de Química, Facultat de Química, Universitat de Barcelona, Any: 2025, Tutora: Júlia Mayans Ayats“In the last decade, S=1/2 systems of Cu (II) complexes and Cu (II) ions in the solid state have been found to exhibit slow magnetic relaxations. With the aim of progressing toward the entanglement of spin states and quantum computing using spin qubits, a greater number of studies on molecule-based spin qubits that exhibit magnetic interactions will be conducted and will be of increasing importance from now on.” (2)
Nickel (II), similarly to copper (II), is a transition metal cation that can show interesting magnetic behaviour when is coordinated with suitable ligands. With an electronic configuration of d8, Ni (II) tends to form stable octahedral geometries, where the presence of unpaired electrons contributes to the magnetic susceptibility of the complex. In polynuclear systems, Ni (II) allows the study of magnetic interactions such as antiferromagnetism, especially when metal centres are connected through bridging ligands like oxalate. Also, its smaller contribution to the Jahn-Teller effect compared to Cu (II) usually results in less distorted structures, which makes the structural and magnetic analysis easier to interpret. (3)
This project is focused on the synthesis of new coordination compounds using copper (II) and nickel (II) salts with nitrogenated macrocycles as ligands, combined with oxalate or benzoquinone bridges. The main objective is to create and study these complexes for their potential magnetic properties, with possible future applications in molecular magnets or quantum technologies.
During the project, six different compounds were successfully synthesised and characterized. The ligands used (232-N4 and 323-N4) helped to build coordination structures with varying geometries. Techniques like IR spectroscopy and X-ray diffraction were used to analyse their structures. In parallel, their magnetic behaviour was studied using SQUID magnetometry, which allowed precise measurements of magnetization and magnetic susceptibility. Additionally, Electron Paramagnetic Resonance (EPR) was carried out.
The complexes showed interesting structural details and magnetic patterns depending on their composition.
Concepts such as magnetization, susceptibility, and anisotropy of the g-factor are essential to interpret the results correctly.
Through these analyses, it is possible to relate geometric features of the complexes with their magnetic responses, which is a key aspect in the field of molecular magnetism.
Although some reactions didn’t give products (which are in the appendix 1), the project contributed valuable knowledge. It supports basic research in coordination chemistry and molecular magnetism, which can be useful in high-density data storage, quantum computing, or advanced sensors in the futur
Síntesi de complexos de coordinació derivats de macrocicles nitrogenats. Estudi magnètic
No full textTreballs Finals de Grau de Química, Facultat de Química, Universitat de Barcelona, Any: 2025, Tutora: Júlia Mayans Ayats“In the last decade, S=1/2 systems of Cu (II) complexes and Cu (II) ions in the solid state have been found to exhibit slow magnetic relaxations. With the aim of progressing toward the entanglement of spin states and quantum computing using spin qubits, a greater number of studies on molecule-based spin qubits that exhibit magnetic interactions will be conducted and will be of increasing importance from now on.” (2)
Nickel (II), similarly to copper (II), is a transition metal cation that can show interesting magnetic behaviour when is coordinated with suitable ligands. With an electronic configuration of d8, Ni (II) tends to form stable octahedral geometries, where the presence of unpaired electrons contributes to the magnetic susceptibility of the complex. In polynuclear systems, Ni (II) allows the study of magnetic interactions such as antiferromagnetism, especially when metal centres are connected through bridging ligands like oxalate. Also, its smaller contribution to the Jahn-Teller effect compared to Cu (II) usually results in less distorted structures, which makes the structural and magnetic analysis easier to interpret. (3)
This project is focused on the synthesis of new coordination compounds using copper (II) and nickel (II) salts with nitrogenated macrocycles as ligands, combined with oxalate or benzoquinone bridges. The main objective is to create and study these complexes for their potential magnetic properties, with possible future applications in molecular magnets or quantum technologies.
During the project, six different compounds were successfully synthesised and characterized. The ligands used (232-N4 and 323-N4) helped to build coordination structures with varying geometries. Techniques like IR spectroscopy and X-ray diffraction were used to analyse their structures. In parallel, their magnetic behaviour was studied using SQUID magnetometry, which allowed precise measurements of magnetization and magnetic susceptibility. Additionally, Electron Paramagnetic Resonance (EPR) was carried out.
The complexes showed interesting structural details and magnetic patterns depending on their composition.
Concepts such as magnetization, susceptibility, and anisotropy of the g-factor are essential to interpret the results correctly.
Through these analyses, it is possible to relate geometric features of the complexes with their magnetic responses, which is a key aspect in the field of molecular magnetism.
Although some reactions didn’t give products (which are in the appendix 1), the project contributed valuable knowledge. It supports basic research in coordination chemistry and molecular magnetism, which can be useful in high-density data storage, quantum computing, or advanced sensors in the futur
Complexos de lantànids amb òxids de fosfina: síntesi, luminescència i magnetisme
No full textTreballs Finals de Grau de Química, Facultat de Química, Universitat de Barcelona, Any: 2024, Tutors: Arnald Grabulosa Rodríguez, Júlia Mayans AyatsLanthanide-based molecular materials have become the focus of attention in numerous fields of research, such as molecular magnetism or luminescence, due to their unique intrinsic properties.
This TFG presents the synthesis and structural, magnetic, and luminescent characterization of a family of molecular complexes based on lanthanide (III) cations. The complexes are formed by the reaction of different lanthanide salts with a phosphine oxide ligand, dppmO2.
These complexes present a neutral mononuclear structure with a nonacoordinated central lanthanide ion by nine O-donor atoms. This structure has been authenticated by X-Ray crystal diffraction of the 5-Tb complex, where the coordination geometry can be described as a monocapped square antiprism.
The magnetic measurements revealed that all the complexes, with the exception of 4-Gd, exhibit high intrinsic single ion anisotropy determined through the D parameter calculated by static measurements. Furthermore, dynamic magnetic measurements demonstrated that 4-Gd, 5-Tb, 8-Yb complexes exhibit slow relaxation of their magnetization, as evidenced by their out-of-phase susceptibility (’’) as a response to an alternating current magnetic field.
The fitting of the dynamic measurements has been performed to elucidate the relaxation mechanisms causing the complexes to lose their magnetization. Complex 5-Tb follows a purely Raman process, whereas 4-Gd and 8-Yb follow a combination between Raman and quantum tunnelling processes. These relaxation mechanisms are mediated by spin-phonon interaction.
Finally, the luminescent measurements revealed visible intrinsic luminescence for both 3-Eu and 5-Tb, indicating that dpmO2, despite being a chromophore, do not perform an efficient effect as sensitizer
Óxidos de fosfina como compuestos luminiscentes para la emisión de luz modulada
Full text linkTreballs Finals de Grau de Química, Facultat de Química, Universitat de Barcelona, Any: 2023, Tutors: Arnald Grabulosa Rodríguez, Júlia Mayans AyatsThis TFG presents the synthesis, the structural characterization, magnetic properties and/or luminescence of 4 compounds: rac-BINAPO2 (1), [Tb(acac)3((R)-BINAPO2)] (2a), [Gd(acac)3((R)-BINAPO2)] (3a) and [Eu(acac)3((R)-BINAPO2)] (4a).These lanthanide complexes were synthesized by reaction of Tb(III), Gd(III) and Eu(III) salts with racemic and enantiopure BINAPO2 (1), which is a chiral ligand.
The structural characterization reveals that the terbium compound (2a) is mononuclear with the formula [Tb(acac)3((R)-1)], with 1 acting as a bidentate ligand by the phosphoryl groups. The complex is octacoordinated to 8 oxygen atoms and the coordination geometry can be described either as a square antiprism (SAPR-8) or a bicapped trigonal prism (BTPR-8).
The magnetic static measurements reveal that 2a exhibit a high intrinsic single ion anisotropy and it does not present SIMs behaviour. Compound 3a follows a Curie law and has an intrinsic single ion isotropic behaviour and show SIMs (Single Ion Magnet) behaviour. The SIMs behaviour can be deduced by the response AC which can be observed on the magnetic dynamic measurements. And the relaxation mechanism process of magnetization has been obtained which follows a Raman and Direct process.
The luminescent measurements were performed for compound 2a and 4a indicated that both complexes have an efficient sensitization effect. This fact it is due to the (R)-1 ligand because is a chromophore.
Finally, the chiroptical properties have been studied for Gd(III) complexes 3a and 3b, containing the R and S enantiomers of 1 respectively. As expected, the two spectra are mirror images, which confirms the analogous structure of 3a and 3b
3d and/or 4f coordination compounds derived from chiral Schiff bases: magnetic and spectroscopic study
Full text linkThis PhD thesis has been developed in the Molecular Magnetism Group of the University of Barcelona.
As its name indicates, the Molecular Magnetism Group is mostly interested in the magnetic study of coordination complexes, mainly with d metals but also with lanthanide cations, which permit magnetic studies but also luminescence studies, which could allow the syntheses of multifunctional products. The group has also interest in supramolecular chemistry and chirality.
The main objective of the thesis was the synthesis, magnetic and spectroscopic characterization of coordination complexes derived from chiral Schiff bases, used as organic ligands, and, due to the chirality of the organic ligands, the study of the chirality transfer from ligand to metal.
This series of organic ligands, have been combined with different metals: With 3d metals, like manganese, iron or nickel, but also with 4f metals or with combinations of both types. The metals used as paramagnetic cations have been used in the search of Single Molecule Magnet (SMM) behavior and also to develop a series of magnetostructural correlations. In other cases, the interesting part of the final product was related with their supramolecular chemistry.
All the products in this thesis have been magnetically characterized to try to elucidate their kind of magnetic interaction (ferromagnetic, antiferromagnetic or ferromagnetic), and, in the case that they present SMM behavior, to study their slow relaxation of the magnetization. Moreover, for complexes derived from lanthanide cations which are highly anisotropic due to the ion itself, other characterization techniques have been performed: Cantilever Torque Magnetometry (CTM) for the complete resolution of the magnetic anisotropy, and spectroscopic techniques like Electronic Paramagnetic Resonance (EPR), in X and W bands, in powder and monocrystal samples.
Due to the chiral nature of the used organic ligands, all the products in this thesis have been characterized by Electronic Circular Dichroism (ECD). This technique has been used to demonstrate the chirality of the products and the differences in the solution vs. solid structures.
The induced chirality in the final products due to the use of enantiopure reactants could allow the future study of the derived properties, like for example the emission of polarized light due to the presence of the lanthanide cation in a chiral environment, or the ferroelectricity, which should achieve the multiferrocity in the final materials.
The thesis contains a final chapter with a discussion about how the different ligands behaved with the different metals, about how the chirality of the reactants affected the final supramolecular structure, demonstrating that the chiral and racemic forms of a reactant not always yield in the same final structure, and about how the metals behave magnetically in each situation.L’objectiu principal de la tesi ha estat la síntesi i caracterització, magnètica i espectroscòpica, de complexes de coordinació derivats de bases de Schiff quirals. Les bases de Schiff han estat sintetitzades, o bé a partir d’una diamina condensada amb dos grups aldehid, o bé a partir d’un aminoalcohol condensat amb un grup aldehid.
Aquesta sèrie de lligands orgànics, s’ha combinat amb diferents metalls, 3d¸4f o barreges dels dos. En d’altres casos, la part que ens ha interessat del complexes sintetitzats ha estat la seva química supramolecular.
Tots els productes has estat caracteritzats magnèticament, per intentar esbrinar el seu tipus d’interacció magnètica (acoblament ferromagnètic, ferrimagnètic o antiferromagnètic) i, en cas de que presentessin propietats d’imant unimolecular, per esbrinar com era la seva relaxació magnètica. A més a més, per als compostos derivats de ions lantànid, que presenten una elevada anisotropia associada al catió, s’han dut a terme altres tècniques de caracterització magnètica, com l’anomenada Cantilever Torque Magnetomentry (CTM), i de caracterització espectroscòpica amb Ressonància Paramagnètica Electrònica (EPR) en banda X i en banda W, tan de compostos en pols com de monocristall.
Degut a la naturalesa quiral dels lligands utilitzats, s’han pogut caracteritzar tots els productes mitjançant Dicroisme Circular Electrònic (ECD), que ens ha servit per demostrar tant la quiralitat dels productes com la seva estructura comparada en sòlid i en dissolució.
La quiralitat induïda als productes mitjançant l’ús de reactius enentiomèricament purs, ha de permetre en el futur estudiar-ne les propietats que se’n deriven, com per exemple l’emissió de llum polaritzada deguda també a la presencia del catió lantànid, o la ferroelectricitat, que permetria aconseguir la síntesis de compostos multiferroics
Synthesis and Magnetic Studies of Quasi-Isotropic Coordination Compounds with 3d and 4f cations
Full text linkPrograma de Doctorat en Nanociències[eng] The present Thesis is entitled “Synthesis and Magnetic Studies of Quasi-Isotropic Coordination Compounds with 3d and 4f cations”. The topic of the Thesis is to prepare coordination compounds of paramagnetic metal cations, either 3d or 4f, with Schiff base ligands, in order to study their magnetic properties and their slow relaxation of magnetization (SRM). The main characteristic of the compounds that show SRM is the presence of magnetic anisotropy, in the form D or axial zero-field splitting, which define the energy barrier that has to be overcome in order to have relaxation of magnetization. This Thesis provide experimental evidence that even if the parameter D can take low values, or even negligible, SRM can happen. This kind of systems belong the family of quasi-isotropic SMMs, because they have as building blocks metal cations that possess very small magnitude of D.
The cations that have been chosen for this research are GdIII and MnII, which contain half- filled f and d orbitals, respectively. GdIII cannot present magnetic anisotropy due to its spherical electronic configuration; MnII has no crystal field stabilization energy, and thus, allowed us to tune its geometry. This fact, helped in order to prove that firstly, low magnetic anisotropy can play a pivotal role for the presence of SRM and secondly, that geometric distortions in cation’s environment are desired in order to observe relaxation of magnetization.
Due to the fact that magnetic anisotropy takes very low values, classical magnetometry cannot give reliable results. Thus, Electronic Paramagnetic Resonance (EPR) measurements were carried out in order to define the axial and rhombic values of anisotropy.[cat] La tesis doctoral “Synthesis and Magnetic Studies of QuasiIsotropic Coordination Compounds with 3d and 4f cations” ha estat duta a terme al laboratori de Magnetisme Molecular del Departament de Química Inorgànica i Orgànica de la Universitat de Barcelona.
La present tesis doctoral estudia la coordinació de lligands tipus Base de Schiff a diferents cations paramagnètics per a estudiar els seu comportament magnetoquímica i la seva relaxació lenta de la magnetització (SMR). Tots els compostos que es presenten han estat sintetitzats, caracteritzats estructuralment i magnèticament.
Un dels paradigmes de la relaxació lenta de la magnetització ha estat sempre la necessària existència d’una elevada anisotropia magnètica (parametritzada com a D o axial zero field splitting) de la quan en depèn la barrera d’energia potencial necessària per a presentar SMR.
La present tesi doctoral, ajuda a demostrar que aquest paràmetre D pot ser gairebé negligible i dóna lloc al que hem anomenat quasi-isotropic slow relaxation, ja que els sistemes que aquí es discuteixen estan derivats de cations paramagnètics isotròpics (i per tant amb una D gairebé negligible) i tot i així presenten comportament SMR.
Els cations escollits per a estudiar la propietat de relaxació lenta en sistemes isotròpics han estat els cations amb capes semiplenes com el MnII i GdIII. El GdIII presenta una distribució electrònica dels seus electrons f completament esfèrica i per tant sense possibilitat d’anisotropia, mentre que el MnII ha permès manipular la seva geometria i camp cristal·lí per demostrar que (i) a mida que s’augmenta la seva anisotropia mitjançant la introducció de diferents àtoms donadors en la seva esfera de coordinació va perdent caràcter de SMR i (ii) que a mida que augmenta la distorsió del seu entorn de coordinació també augmenta el seu caràcter SMR.
Les mesures acurades del comportament SMR s’han realitzat amb SQUID. Degut a que aquesta classe de SMR no pot transcórrer a través de la barrera d’energia potencial, mesures específiques d’espectroscòpies d’ultra baixa freqüència han demostrat que, efectivament, els mecanismes de relaxació magnètica no transcorren a través d’una barrera energètica. L’anisotropia magnètica dels compostos s’ha mesurat mitjançant mesures d’EPR
Synthesis and Magnetic Studies of Quasi-Isotropic Coordination Compounds with 3d and 4f cations
Full text link[eng] The present Thesis is entitled “Synthesis and Magnetic Studies of Quasi-Isotropic Coordination Compounds with 3d and 4f cations”. The topic of the Thesis is to prepare coordination compounds of paramagnetic metal cations, either 3d or 4f, with Schiff base ligands, in order to study their magnetic properties and their slow relaxation of magnetization (SRM). The main characteristic of the compounds that show SRM is the presence of magnetic anisotropy, in the form D or axial zero-field splitting, which define the energy barrier that has to be overcome in order to have relaxation of magnetization. This Thesis provide experimental evidence that even if the parameter D can take low values, or even negligible, SRM can happen. This kind of systems belong the family of quasi-isotropic SMMs, because they have as building blocks metal cations that possess very small magnitude of D.
The cations that have been chosen for this research are GdIII and MnII, which contain half- filled f and d orbitals, respectively. GdIII cannot present magnetic anisotropy due to its spherical electronic configuration; MnII has no crystal field stabilization energy, and thus, allowed us to tune its geometry. This fact, helped in order to prove that firstly, low magnetic anisotropy can play a pivotal role for the presence of SRM and secondly, that geometric distortions in cation’s environment are desired in order to observe relaxation of magnetization.
Due to the fact that magnetic anisotropy takes very low values, classical magnetometry cannot give reliable results. Thus, Electronic Paramagnetic Resonance (EPR) measurements were carried out in order to define the axial and rhombic values of anisotropy.[cat] La tesis doctoral “Synthesis and Magnetic Studies of QuasiIsotropic Coordination Compounds with 3d and 4f cations” ha estat duta a terme al laboratori de Magnetisme Molecular del Departament de Química Inorgànica i Orgànica de la Universitat de Barcelona.
La present tesis doctoral estudia la coordinació de lligands tipus Base de Schiff a diferents cations paramagnètics per a estudiar els seu comportament magnetoquímica i la seva relaxació lenta de la magnetització (SMR). Tots els compostos que es presenten han estat sintetitzats, caracteritzats estructuralment i magnèticament.
Un dels paradigmes de la relaxació lenta de la magnetització ha estat sempre la necessària existència d’una elevada anisotropia magnètica (parametritzada com a D o axial zero field splitting) de la quan en depèn la barrera d’energia potencial necessària per a presentar SMR.
La present tesi doctoral, ajuda a demostrar que aquest paràmetre D pot ser gairebé negligible i dóna lloc al que hem anomenat quasi-isotropic slow relaxation, ja que els sistemes que aquí es discuteixen estan derivats de cations paramagnètics isotròpics (i per tant amb una D gairebé negligible) i tot i així presenten comportament SMR.
Els cations escollits per a estudiar la propietat de relaxació lenta en sistemes isotròpics han estat els cations amb capes semiplenes com el MnII i GdIII. El GdIII presenta una distribució electrònica dels seus electrons f completament esfèrica i per tant sense possibilitat d’anisotropia, mentre que el MnII ha permès manipular la seva geometria i camp cristal·lí per demostrar que (i) a mida que s’augmenta la seva anisotropia mitjançant la introducció de diferents àtoms donadors en la seva esfera de coordinació va perdent caràcter de SMR i (ii) que a mida que augmenta la distorsió del seu entorn de coordinació també augmenta el seu caràcter SMR.
Les mesures acurades del comportament SMR s’han realitzat amb SQUID. Degut a que aquesta classe de SMR no pot transcórrer a través de la barrera d’energia potencial, mesures específiques d’espectroscòpies d’ultra baixa freqüència han demostrat que, efectivament, els mecanismes de relaxació magnètica no transcorren a través d’una barrera energètica. L’anisotropia magnètica dels compostos s’ha mesurat mitjançant mesures d’EPR
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Linked Nickel Metallacrowns from a Phosphonate/2-Pyridyloximate Blend of Ligands: Structure and Magnetic Properties
Full text linkIn the present work, four new NiII clusters with nuclearities ranging between Ni4 and Na2Ni8 were synthesized, employing the versatile ligand phenylphosphonate and 6-methylpyridylaldoximate as the coligand. Crystallographic data show that the tetranuclear complex [Ni 4 (6-MepaoH)4(PhPO3)2(OH)2(MeOH)4](OH)2 (1) consists of two dimers linked by phosphonate bridges, whereas [Cs2Ni6(6-Mepao)6(PhPO3)3(OH)2(H2O)8] (2), Cs[Ni8(6-MepaoH)6(6-Mepao)6(PhPO3)3](ClO4)5 (3), and [Ni8Na2(BzO)6(6-Mepao)6(PhPO3)3] (4) are built from phosphonato-linked {Ni3(6-Mepao)3} metallacycles. The [9-MCNiII(6‑Mepao)-3] fragments in 2−4 show the unusual coordination of additional Cs+, Na+ , and/or NiII cations. Direct-current magnetic measurements were carried in the 300−2 K range. Analysis of the experimental data revealed a complex response with strong antiferromagnetic interactions mediated by the oximato bridges and weak interactions mediated by the phosphonate ones
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