5 research outputs found

    Theoretical Prediction of Spin-Crossover Temperatures in Ligand-Driven Light-Induced Spin Change Systems

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    Spin-crossover compounds exhibit two alternative spin states with distinctive chemical and physical properties, a particular feature that makes them promising materials for nanotechnological applications as memory or display devices. A key parameter that characterizes these compounds is the spin-crossover temperature, <i>T</i><sub>1/2</sub>, defined as the temperature with equal populations of high and low-spin species. In this study, a theoretical/computational approach is described for the calculation of <i>T</i><sub>1/2</sub> for the <i>trans</i>-[FeĀ­(styrylpyridine)<sub>4</sub>(NCX)<sub>2</sub>] (X = S, Se, and BH<sub>3</sub>, styrylpyridine in the <i>trans</i> configuration) ligand driven light-induced spin change (LD-LISC) complexes. In all cases, the present calculations provide an accurate description of both structural and electronic properties of the LD-LISC complexes and, importantly, predict spin-crossover temperatures in good agreement with the corresponding experimental data. Fundamental insights into the dependence of <i>T</i><sub>1/2</sub> on the nature of the axial ligands are obtained from the direct analysis of the underlying electronic structure in terms of the relevant molecular orbitals

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

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    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 (<i>T</i><sub>1/2</sub>), a key physical quantity in the characterization of spin-crossover systems, for the family of tetracoordinated Fe<sup>II</sup> transition-metal complexes of generic formula [PhBĀ­(MesIm)<sub>3</sub>Ā­FeNPR<sub>1</sub>R<sub>2</sub>R<sub>3</sub>]. Our calculations correctly reproduce the experimentally reported decrease in the <i>T</i><sub>1/2</sub> with an increasing size of the phosphine and allow for the prediction of the <i>T</i><sub>1/2</sub> 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 <i>T</i><sub>1/2</sub> 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<sup>R</sup>)<sub>2</sub>Mn] Manganocenes

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    A computational study of the spin-crossover behavior in the family [(Cp<sup>R</sup>)<sub>2</sub>Mn] (R = Me, <sup><i>i</i></sup>Pr, <sup><i>t</i></sup>Bu) is presented. Using the OPBE functional, the different electronic and steric effects over the metalā€™s ligand field are studied, and trends in the spin-crossover-temperature (<i>T</i><sub>1/2</sub>) 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 (<i>T</i><sub>1/2</sub>) 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 <i>T</i><sub>1/2</sub> 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

    Theoretical Modeling of Spin Crossover in Metalā€“Organic Frameworks: [Fe(pz)<sub>2</sub>Pt(CN)<sub>4</sub>] as a Case Study

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    Metalā€“organic frameworks (MOFs) with spin-crossover behavior are promising materials for applications in memory storage and sensing devices. A key parameter that characterizes these materials is the transition temperature <i>T</i><sub>1/2</sub>, defined as the temperature with equal populations of low-spin and high-spin species. In this study, we describe the development, implementation, and application of a novel hybrid Monte Carlo/molecular dynamics method that builds upon the Ligand Field Molecular Mechanics approach and enables the modeling of spin-crossover properties in bulk materials. The new methodology is applied to the study of a spin-crossover MOF with molecular formula [FeĀ­(pz)<sub>2</sub>PtĀ­(CN)<sub>4</sub>] (pz = pyrazine). The total magnetic moment of the material is determined as a function of the temperature from direct calculations of the relative equilibrium populations of both low-spin and high-spin states of each FeĀ­(II) center of the framework. The <i>T</i><sub>1/2</sub> value, calculated from the temperature dependence of the magnetization curve, is in good agreement with the available experimental data. A comparison between the spin-crossover behavior of the isolated secondary building block of the framework and the bulk material is presented, which reveals the origin of the different spin-crossover properties of the isolated molecular system and corresponding MOF structure

    Non-Switching 1,2-Dithienylethene-based Diplatinum(II) Complex Showing High Cytotoxicity

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    A diplatinumĀ­(II) complex was prepared from a new 1,2-dithienylethene-based ligand containing <i>N</i>-methylimidazole groups as metal-binding units. Reaction of the ligand 1,2-bisĀ­[2-methyl-5-(1-methyl-1<i>H</i>-imidazol-2-yl)-3-thienyl]-cyclopentene (<b>L2</b><sup><b>H</b></sup>) with <i>cis</i>-dichlorobisĀ­(dimethylsulfoxido)Ā­platinumĀ­(II) generated the bimetallic complex <i>trans</i>-[Pt<sub>2</sub>Cl<sub>4</sub>(DMSO)<sub>2</sub>(<b>L2</b><sup><b>H</b></sup>)] (DMSO = dimethyl sulfoxide), whose DNA-interacting properties were investigated using different techniques. Cytotoxicity assays with various cancer cell lines showed that this compound is active, with IC<sub>50</sub> values in the micromolar range. Surprisingly, the diplatinumĀ­(II) complex does not exhibit the anticipated photoswitching properties; indeed, UV irradiation does not lead to the photocyclization of the ligand <b>L2</b><sup><b>H</b></sup> or of the metal complex. Computational studies were performed and revealed significant differences in the electronic structure of <b>L2</b><sup><b>H</b></sup> compared with <b>L1</b><sup><b>H</b></sup> (i.e., 1,2-bisĀ­[2-methyl-5-(4-pyridyl)-3-thienyl]-cyclopentene, which exhibits photoswitching properties), in terms of the relevant molecular orbitals involved in the UVā€“vis absorption features, which ultimately is responsible for the inertia of <b>L2</b><sup><b>H</b></sup> toward photocyclization
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