Química de coordinación de un ligando derivado de tripticeno: en la búsqueda de sensores ópticos

Traballo Fin de Grao en Química. Curso 2013-2014The present work describes the synthesis of the new Schiff base H2L, containing a trypticene residue, and its reactivity towards niquel(II), copper(II), zinc(II), palladium(II), silver(I) and cadmium(II). This study discusses the reaction conditions that allow isolating trinuclear Zn and Ni complexes. The experimental requirements to obtain coordination compounds with the remaining metal ions, although sought, could not be set. Analytical and spectrometric characterization of the Zn and Ni compounds completely agrees with the trinuclear nature of the complexes. The fluorescence study of the ligand in solution, both as free ligand and in the presence of ZnII and NiII, shows that H2L is fluorescent and that the presence of the metal ions partially quenches the fluorescence emission of the ligand itself. Thus, given the variation of the luminescence properties in the presence of metal ions, the ability of H2L to act as a luminescence chemosensor was investigated. The results show that the experimental conditions tested do not permit to stabilize the optical response of the ligand in the presence of metal ions. In addition, H2L was checked as an absorbance chemosensor, and in this case the results demonstrate that it can be used to quantify the presence of Zn2+ and Ni2+ in the medium

Anisotropía Magnética en Imanes Moleculares y Qubits con Complejos Metálicos de Espín ½

[spa] Esta tesis presenta una serie de estudios computacionales basados en métodos de estructura electrónica en los que se analizan la anisotropía magnética y las propiedades derivadas de esta en complejos magnéticos candidatos a imán molecular y bit cuántico con la particularidad de tener un espín total S = ½. En los primeros tres capítulos de esta tesis se estudian complejos de metales de transición. Por otro lado, el cuarto y último capítulo se centra en analizar complejos de lantánidos, concretamente de YbIII. En el primer capítulo se incluye un trabajo a través del cual se relaciona la configuración electrónica y la geometría de coordinación de un compuesto con su anisotropía magnética, en la forma del tensor g. Se puede establecer dicha conexión gracias a la dependencia del tensor g con la energía de los orbitales d. Esta energía se obtiene mediante cálculos ab initio analizados con el modelo de AILFT. Estos se realizan a partir de la función de onda obtenida en cálculos NEVPT2 realizados en modelos sencillos [MIILn], siendo MII el correspondiente metal divalente de la primera serie de transición con S = ½, L ligandos NH3 Cl- y n un número de coordinación entre 2 y 8. La observación de una anisotropía magnética de eje fácil fuerte indicar la presencia de un posible imán unimolecular mientras que una anisotropía débil es adecuada para presentar comportamiento de bit cuántico. El segundo capítulo realizado en colaboración con el grupo de “Molecular Magnetism and Quantum Computing” dirigido por el Dr. Alejandro Gaita Ariño del Institut de Ciència Molecular de Valencia (ICMol), se centra en el estudio del acoplamiento espín-fonón en tres bits cuánticos de VIV: [VOPc], [VO(dmit)2]2- y [V(dmit)3]2- donde Pc es el ligando ftalocianina y dmit es el ligando 2-tioxo-1,3-ditiol-4,5-ditiolato. A través de la variación que se produce en la anisotropía magnética al deformarmse las distintas moléculas debido al movimiento de cada modo vibracional, se calculó la fuerza del acoplamiento espín-fonón correspondiente a los distintos estados vibracionales, mediante cálculos a nivel NEVPT2/AILFT. Esta magnitud se utilizó para entender las diferencias en los tiempos de coherencia para los distintos sistemas estudiados. El tercer capítulo, finalizando el bloque dedicado a metales de transición, recopila una serie de colaboraciones con distintos grupos experimentales. Se realizó un análisis computacional similar al delos capítulos anteriores para cada compuesto en concreto: estudio de la estructura electrónica mediante cálculos NEVPT2/AILFT, anisotropía magnética en base a los orbitales d de cada compuesto, y comparación de las distintas propiedades magnéticas calculadas con las medidas experimentales. Además, se realizó el ajuste de los tiempos de relajación del espín, examinando los distintos mecanismos de relajación posibles en cada caso. En el último capítulo se analizó el caso del YbIII, un lantánido con S = ½, haciendo uso de cálculos CASPT2+RASSI con el programa MOLCAS. Dichos cálculos de estructura electrónica se realizaron en una serie de modelos [Yb(H2O)n]3+ y [Yb(OH)3(H2O)n-3], utilizando geometrías ideales para números de coordinación entre 2 y 10. Estos cálculos muestran el efecto de la geometría de coordinación y la distribución de carga de los ligandos sobre propiedades fundamentales como la energía de los distintos estados electrónicos, la anisotropía magnética del estado fundamental, o las probabilidades para los distintos mecanismos de relajación. A partir de estos resultados se explican las propiedades como imanes unimoleculares de los sistemas de YbIII encontrados en la bibliografía y se propusieron una serie de geometrías adecuadas para el fenómeno de imán unimolecular en estos sistemas.[eng] This thesis presents a series of theoretical studies based on electronic structure methods to analyze the magnetic anisotropy and other related properties of magnetic complexes with total spin S = ½. The first three chapters are devoted to transition metal complexes while the fourth one addresses lanthanides systems, specifically YbIII. The first chapter determines a relationship between the d orbitals occupation and the coordination geometry of S = ½ transition metal complexes with their magnetic anisotropy, through its g-tensor. This connection is possible due to the relationship between the g-tensor and the splitting of the d manyfold. These energies were obtained using NEVPT2/AILFT calculation on [MIILn] models, screening for different MII metals, coordination numbers (n) and geometries, and ligand nature (L = NH3 or Cl-). The second chapter is a study carried out in collaboration with Dr. Gaita Ariño’s group from the molecular Science Institute of Valencia (ICMol) analyzing the spin-phonon coupling in three VIV qubits: [VOPc], [VO(dmit)2]2- y [V(dmit)3]2-, being Pc = Phthalocyanine and dmit = 1,3-dithiole-2-thione-4,5-dithiolate. In order to analyze the spin-phonon coupling we examined the variation of the magnetic anisotropy using NEVPT2/AILFT calculations for each vibrational mode. The spin-phonon coupling constants obtained for the vibrational modes in the three complexes were used to rationalize their different decoherence times. The third chapter, the last one dedicated to transition metal complexes, compiles a series of collaborations with experimental groups. In these studies, using the same methods as in the previous chapters, we analyzed the electronic structure and magnetic properties of the compounds, explaining experimental results through theoretical calculations. Also, we fitted the spin relaxation times considering the all possible spin relaxation mechanisms. Finally, the fourth chapter explores the magnetic anisotropy and electronic structure of YbIII compounds on the basis of theoretical calculations in a series of [Yb(H2O)n]3+ y [Yb(OH)3(H2O)n-3] model using ideal geometries corresponding to coordination numbers between 2 and 10. These calculations explain the properties of the YbIII single-molecul

Mononuclear lanthanide complexes with 18-crown-6 ether: synthesis, characterization, magnetic properties, and theoretical studies

A family of lanthanide metal complexes with general formula [Ln(H2O)3(18-crown-6)](ClO4)3 (Ln: TbIII, DyIII, ErIII and YbIII) has been synthesized. Their magnetic properties have been characterized by DC and AC SQUID measurements and analyzed with the help of CASSCF-type calculations. The DyIII and YbIII compounds show slow relaxation of the magnetization under an external magnetic field. The analysis of the dependence of the relaxation time with the temperature and external magnetic field reveals that the main contributions are respectively the quantum tunneling and the Raman term, respectively. The analysis of the beta electron density and electrostatic potentials indicate that the axial ligands (three water molecules) generate a relatively small repulsion with the lanthanide electron density being the reason of the moderate magnetic anisotropy found in these systems

Spin-phonon coupling and slow-magnetic relaxation in pristine ferrocenium

We report the spin dynamic properties of non-substituted ferrocenium complexes. Ferrocenium shows a field-induced single-molecule magnet behaviour in DMF solution while cobaltocene lacks slow spin relaxation neither in powder nor in solution. Multireference quantum mechanical calculations give a non-Aufbau orbital occupation for ferrocenium with small first excitation energy that agrees with the relatively large measured magnetic anisotropy for a transition metal S=1/2 system. The analysis of the spin relaxation shows an important participation of quantum tunnelling, Raman, direct and local-mode mechanisms which depend on temperature and the external field conditions. The calculation of spin-phonon coupling constants for the vibrational modes shows that the first vibrational mode, despite having a low spin-phonon constant, is the most efficient process for the spin relaxation at low temperatures. In such conditions, vibrational modes with higher spin-phonon coupling constants are not populated. Additionally, the vibrational energy of this first mode is in excellent agreement with the experimental fitted value obtained from the local-mode mechanism

Computational and Experimental Studies Into the Conformations of a Triptycene-Based Ditopic Ligand

The 18th International Electronic Conference on Synthetic Organic Chemistry session Computational ChemistryWe present a combined computational and experimental study of the possible conformations adopted by a ditopic Schiff base ligand based on triptycene. We have performed DFT calculations on a Y-shaped Schiff base ligand derived from the condensation of 2,6-diaminotriptycene and 2 hydroxybenzaldehyde to obtain the relative energies of their conformers anti-s-cis, syn and anti-s-trans. Since these conformations are practically isoenergetic, interconversions of conformers proceed by rotation about C-N single bonds. NMR spectroscopy shows the presence in solution of the syn conformer, which is stable at room temperature on the NMR time scal

Slow-spin relaxation of a low-spin S = 1/2 FeIII carborane complex

In this communication, we report the first evidence of slow-spin relaxation of a low-spin FeIII carborane complex. Iron S=1/2 complexes showing such behaviour are specially appealing as qubits candidates because they fulfil some of the main requirements to reach long decoherence times: moderate magnetic anisotropy, small spin, metal element mainly with zero-nuclear spin and furthermore, large versatility to introduce chemical modifications

[UF6](2-): A molecular hexafluorido actinide(IV) complex with compensating spin and orbital magnetic moments

The first structurally characterized hexafluorido complex of a tetravalent actinide ion, the [UF6]2- anion, is reported in the (NEt4)2[UF6]2H2O salt (1). The weak magnetic response of 1 results from both U(IV) spin and orbital contributions, as established by combining X-ray magnetic circular dichroism (XMCD) spectroscopy and bulk magnetization measurements. The spin and orbital moments are virtually identical in magnitude, but opposite in sign, resulting in an almost perfect cancellation, which is corroborated by ab initio calculations. This work constitutes the first experimental demonstration of a seemingly non-magnetic molecular actinide complex carrying sizable spin and orbital magnetic moments

A low spin manganese(IV) nitride single molecule magnet

Structural, spectroscopic and magnetic methods have been used to characterize the tris(carbene) borate compound PhB(MesIm)(3)Mn equivalent to N as a four-coordinate manganese(IV) complex with a low spin (S = 1/2) configuration. The slow relaxation of the magnetization in this complex, i.e. its single-molecule magnet (SMM) properties, is revealed under an applied dc field. Multireference quantum mechanical calculations indicate that this SMM behavior originates from an anisotropic ground doublet stabilized by spin-orbit coupling. Consistent theoretical and experiment data show that the resulting magnetization dynamics in this system is dominated by ground state quantum tunneling, while its temperature dependence is influenced by Raman relaxation