5 research outputs found
Theoretical Prediction of Spin-Crossover Temperatures in Ligand-Driven Light-Induced Spin Change Systems
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
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
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 metalās 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 MetalāOrganic Frameworks: [Fe(pz)<sub>2</sub>Pt(CN)<sub>4</sub>] as a Case Study
Metalāorganic 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
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 UVāvis absorption features, which
ultimately is responsible for the inertia of <b>L2</b><sup><b>H</b></sup> toward photocyclization