Theoretical Modeling of the Ligand-Tuning Effect over the Transition Temperature in Four-Coordinated Fe-II Molecules

Spin-crossover molecules are systems of great interest due to their behavior as molecular level switches, which makes them promising candidates for nanoscale memory devices, among other applications. In this paper, we report a computational study for the calculation of the transition temperature (T-1/2), a key physical quantity in the characterization of spin-crossover systems, for the family of tetracoordinated Feu transition-metal complexes of generic formula [PhB(MesIm)(FeNPR1R2R3)-Fe-3]. Our calculations correctly reproduce the experimentally reported decrease in the T-1/2 with an increasing size of the phosphine and allow for the prediction of the T-1/2 in new members of the family that are not reported so far. More importantly, further insight into the factors that control the fine-tuning of the T-1/2 can be obtained by direct analysis of the underlying electronic structure in terms of the relevant molecular orbitals

Electronic and steric control of the spin-crossover behavior in [(Cp-R)(2)Mn] manganocenes

A computational study of the spin-crossover behavior in the family [(Cp-R)(2)Mn] (R = Me, Pr-i, Bu-t) is presented. Using the OPBE functional, the different electronic and steric effects over the metal's ligand field are studied, and trends in the spin-crossover-temperature (T-1/2) behavior are presented in terms of the cyclopentadienyl (Cp) ligand functionalization. Our calculations outlined a delicate balance between both electronic and steric effects. While an increase in the number of electron donating groups increases the spin-crossover temperature (T-1/2) to the point that the transition is suppressed and only the low-spin state is observed, steric effects play an opposite role, increasing the distance between the Cp rings, which in turns shifts T-1/2 to lower values, eventually stabilizing the high-spin state. Both effects can be rationalized by exploring the electronic structure of such systems in terms of the relevant d-based molecular orbitals

CARMEN MARRERO [Material gráfico]

ÁLBUM FAMILIAR CASA DE COLÓNCopia digital. Madrid : Ministerio de Educación, Cultura y Deporte. Subdirección General de Coordinación Bibliotecaria, 201

Theoretical modeling of two-step spin-crossover transitions in FeII dinuclear systems

A computational methodology to model the spin-transition in the dinuclear iron(II) systems [Fe(bt)(NCX)2]2(μ-bpym) and [Fe(pypzH)(NCX)]2(μ-pypz)2 (X = S, Se or BH3) is presented. Using the hybrid meta-GGA exchange-correlation functional TPSSh, accurate values for the thermochemical quantities associated with the different spin-states can be computed, and subsequently used to calculate the corresponding transition temperatures. This results also allow for the correct modeling of the spin-crossover curve, in agreement with the two-step or single-step nature experimentally reported for the transition. Our results indicate that the presence or absence of a two-step transition is mostly dominated by electronic effects and cooperativity between binding pockets plays a minor role. Insight in the electronic structure effects that enhance or suppress this behavior and its origins can be outlined from direct analysis of the relevant d-based molecular orbitals, which allows for a quantitative computational prediction to screen for new dinuclear systems with selected properties

Assessment of the SCAN Functional for Spin-State Energies in Spin-Crossover Systems

The Strongly-Constrained and Appropriately Normed (SCAN) functional has been tested towards the calculation of spin-state energy differences in a dataset of 20 spin-crossover (SCO) systems, ranging from d4 to d7. The results shown that SCAN functional is able to correctly predict the low-spin state as the ground state for all systems, and the energy window provided by the calculations falls in the approximately range of energies that will allow for SCO to occur. Moreover, because SCAN is a pure meta-GGA functional, one can use such method in periodic calculations, accounting for the effect of collective crystal vibrations and counterions in the thermochemistry of the spin-transition. Our results validate this functional as a potential method for in silico screening of new SCO systems at both, molecular and crystal packed levels

Computational Modeling of Transition Temperatures in Spin-Crossover Systems

A survey of different computational approaches to compute thermochemical properties and, in particular, transition temperatures (T1/2) in spin-crossover (SCO) systems is presented. Asides from the possibility of computing accurate values, this work centers its efforts in the use of such computational tools to explain trends in different families of SCO systems, aiming to understand the impact that chemical modifications (both electronic and steric) have over the ligand-field around the metal center, and how such effects can tune the corresponding T1/2. By using concepts from molecular orbital theory combined with the results from the calculations, a simple yet accurate depiction of the shift in T1/2 can be explai

Benchmarking de Herramientas Forenses para Móviles

Actualmente, y cada día con más importancia, los dispositivos móviles (Smartphones y tablets) se han convertido en una herramienta indispensable en las labores diarias tanto a nivel corporativo y personal. Estos dispositivos no solo son capaces de almacenar información referente a la agenda de contactos o reproductor de música y vídeo, sino que son capaces de almacenar una gran cantidad de información que puede resultar ser muy útil en un caso de la informática forense. Nos enfrentamos a grades desafíos como es BYOD ( Bring of your device) está política está haciendo grandes cambios en el mundo de los negocios ya que alrededor de un 90% de los empleados (en los países desarrollados) utilizan sus equipos de algún modo para acceder a la información de la empresa. En la mayoría de los casos las empresas no pueden cambiar esta tendencia. Algunos creen que BYOD ayuda a los empleados a ser más productivos otros creen que eleva la moral de los empleados ya que se permite la flexibilidad dentro de la empresa, pero otro punto de vista es que esto vuelve frágil la Seguridad de la Información y puede vulnerarse la seguridad a través de estos dispositivos. En este proyecto se ha realizado la evaluación de dos suites que poseen diferentes herramientas forenses para dispositivos móviles y una herramienta especializada en extracción de datos, para ello se presenta una breve descripción de la arquitectura de los móviles Android, una breve descripción de las herramientas evaluadas, metodología utilizada para la realización del benchmarking, exponiendo los criterios utilizados para posteriormente presentar el análisis de los resultados obtenidos y algunas recomendaciones que son de mucha importancia para este estudi

Spin dynamics in single-molecule magnets and molecular qubits

Over recent decades, much effort has been made to lengthen spin relaxation/decoherence times of single-molecule magnets and molecular qubits by following different chemical design rules as maximizing the total spin value, controlling symmetry, enhancing the ligand field or inhibiting key vibrational modes. Simultaneously, electronic structure calculations have been employed to provide an understanding of the processes involved in the spin dynamics of molecular systems and served to refine or introduce new design rules. This review focuses on contemporary theoretical approaches focused on the calculation of spin relaxation/decoherence times, highlighting their main features and scope. Fundamental aspects of experimental techniques for the determination of key Single Molecule Magnet/Spin Qubit properties are also reviewed

Can theoretical methods go beyond the experimental data? The case of molecular magnetism.

International audienceThe complexity of polynuclear transition metal complexes with the most appealing magnetic properties makes it impossible to extract the values of exchange interactions between the paramagnetic centers using experimental techniques. Hence, theoretical methods based on density functional theory are used because they allow the accurate estimation of such values. Three Mn(6) complexes were studied and the calculated exchange coupling constants used to plot a magnetic susceptibility curve that can be compared with the experimental ones. We propose a new tool to facilitate the understanding of the magnetic properties in systems of this kind. We employed magnetostructural maps to correlate the calculated exchange coupling constants with structural parameters for the dinuclear or polynuclear manganese complexes that we have studied

TEJEDA [Material gráfico]

Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte. Subdirección General de Coordinación Bibliotecaria, 201