Tuning the spin-crossover properties of [Fe] metal-organic cages.

A computational study on the interplay between ligand functionalization and guest effects on the transition temperature () in the [Fe(L)]@X (L = 1,3-bis-(3-(pyridin-2-yl)-1-pyrazol-5-yl)benzene, X = H, F, Cl, Br, I and [BF], R = H, F, or CH) family of metal-organic cages (MOCs) is presented. Our results indicate that ligand functionalization with electron-donating or electron-withdrawing groups can significantly impact the as expected, while the guest effect in lowering the has a linear correlation with the increasing guest size. More importantly, small guests can move away from the center of the cavity, thus enhancing the two-step characteristic of the transition.

Synthesis and characterization of highly diluted polyanionic iron(II) spin crossover systems.

Spin crossover (SCO) complexes, through their reversible spin transition under external stimuli, can work as switchable memory materials. Here, we present a protocol for the synthesis and characterization of a specific polyanionic iron SCO complex and its diluted systems. We describe steps for its synthesis and the determination of crystallographic structure of the SCO complex in diluted systems.

Fine-tuning of the spin-crossover properties of Fe(III) complexes ligand design.

Exploring the chemical space of a given ligand aiming to modulate its ligand field strength is a versatile strategy for the fine-tuning of physical properties such as the transition temperature () of spin-crossover (SCO) complexes. The computational study presented herein aims at systematically exploring the extent to which the ligand substituent effects can modulate in two families of Fe(III) SCO systems with a NO coordination environment and at identifying the best descriptors for fast and accurate prediction of changes in upon ligand functionalization. B3LYP* calculations show that the attachment of substituents to β-ketoiminato fragments (L) leads to drastic changes in , while functionalization of phenolato moieties (L) allows for a finer degree of control over .

Elucidating the exchange interactions in a {GdCu} propellor.

The multinucleating ligand 2,2'-(propane-1,3-diyldiimino)bis[2-(hydroxymethyl)-propane-1,3-diol] (bis-tris propane, HL) is used in the design of a new family of 3d-4f complexes that display an unusual {LnCu} four-blade propeller topology. We report the synthesis, structure and magnetic characterisation of [LnCu(HL)](Cl)(ClO)·6CHOH, where Ln = Gd (1), Tb (2), Dy (3), La (4). Previously we have used CHCOO and NO as co-ligands with bis-tris propane, but here the use of Cl and ClO leads to coordination of four {Cu(HL)} units around the central Ln ion.

Push and Pull Effect of Methoxy and Nitro Groups Modifies the Spin-State Switching Temperature in Fe(III) Complexes.

We have explored the impact of electron-donating (methoxy) and electron-withdrawing (nitro) substituents on SalEen ligand based spin crossover (SCO) behavior of Fe(III) complexes. Thus, 3-X-substituted SalEen ligands were employed to prepare [Fe(3-X-SalEen)]·NCSe, where X = OMe (), H (), and NO () (3-X-SalEen is the condensation product of 3-substituted salicylaldehyde and -ethylethylenediamine). The characteristic spin transition temperature ( ) is shown to shift to a lower temperature when an electron-donating substituent (OMe) is used and to a higher temperature when an electron-withdrawing substituent (NO) is used.

Accurate calculation of spin-state energy gaps in Fe(III) spin-crossover systems using density functional methods.

Fe(III) complexes are receiving ever-increasing attention as spin crossover (SCO) systems because they are usually air stable, as opposed to Fe(II) complexes, which are prone to oxidation. Here, we present the first systematic study exclusively devoted to assess the accuracy of several exchange-correlation functionals when it comes to predicting the energy gap between the high-spin ( = 5/2) and the low-spin ( = 1/2) states of Fe(III) complexes. Using a dataset of 24 different Fe(III) hexacoordinated complexes, it is demonstrated that the B3LYP* functional is an excellent choice not only for predicting spin-state energy gaps for Fe(III) complexes undergoing spin-transitions but also for discriminating Fe(III) complexes that are either low- or high-spin in the whole range of temperatures.

Controlling the spin-crossover behavior of the [Cr(indenyl)] family ligand functionalization.

In this work, a computational method to study the spin-crossover (SCO) behavior of the [Cr(n-Meindenyl)2] family was carried out. Using the TPSSh/Def2TZVP method with the GD3BJ dispersion correction scheme, we computed the thermochemistry and transition temperatures (T1/2) for all members of this family, which are in excellent agreement with the available experimental data. Moreover, the computed data allow us to build a model that describes the effect of functionalizing the indenyl ligand in different positions on the spin-state energy gap and transition temperature.

Piano-Stool Ruthenium(II) Complexes with Delayed Cytotoxic Activity: Origin of the Lag Time.

We have recently reported a series of piano-stool ruthenium(II) complexes of the general formula [RuCl(η-arene)(P(1-pyrenyl)RR)] showing excellent cytotoxic activities (particularly when R = R = methyl). In the present study, new members of this family of compounds have been prepared with the objective to investigate the effect of the steric hindrance of a bulky phosphane ligand, namely diisopropyl(1-pyrenyl)phosphane (), on exchange reactions involving the coordinated halides (X = Cl, I). Two η-arene rings were used, i.

Electronic Control of Spin-Crossover Properties in Four-Coordinate Bis(formazanate) Iron(II) Complexes.

The transition between spin states in d-block metal complexes has important ramifications for their structure and reactivity, with applications ranging from information storage materials to understanding catalytic activity of metalloenzymes. Tuning the ligand field (Δ) by steric and/or electronic effects has provided spin-crossover compounds for several transition metals in the periodic table, but this has mostly been limited to coordinatively saturated metal centers in octahedral ligand environments. Spin-crossover complexes with low coordination numbers are much rarer.

[Co/Fe(α-Alkyl-tpdt)]: Alkyl-Substituted Cobalt and Iron Bis-dithiolenethiophenic Complexes.

Tetraphenylphosphonium salts of Co and Fe complexes with alkyl-substituted, -butyl (), and isopropyl () 2,3-thiophenedithiolate (α-tpdt) ligands, namely, TPP[Co(α--tpdt)] (), TPP[Fe(α--tpdt)] (-), TPP[Co(α--tpdt)] (), and TPP[Fe(α--tpdt)] () were prepared and characterized by cyclic voltammetry, single crystal X-ray diffraction, magnetic susceptibility measurements, and Fe Mössbauer spectroscopy. Compound and are isostructural with their Au and Ni analogues with a square-planar coordination geometry. Compound presents two polymorphs (-) both showing a Fe(III) bisdithiolene dimerization.

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

The strongly constrained and appropriately normed (SCAN) functional has been tested toward the calculation of spin-state energy differences in a data set of 20 spin-crossover (SCO) systems, ranging from d to d. Results show that the 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 approximate range of energies that will allow for SCO to occur. Moreover, the SCAN functional can be used in periodic boundary condition calculations, accounting for the effect of collective crystal vibrations and counterions in the thermochemistry of the spin transition.

Thermal spin crossover in Fe(ii) and Fe(iii). Accurate spin state energetics at the solid state.

The thermal spin crossover (SCO) phenomenon refers to an entropy-driven spin transition in some materials based on d6-d9 transition metal complexes. While its molecular origin is well known, intricate SCO behaviours are increasingly common, in which the spin transition occurs concomitantly to e.g.

Computational assessment on the Tolman cone angles for P-ligands.

The Tolman cone angle (θ), the par excellence descriptor of the steric measure of a phosphine, has been recomputed for a set of 119 P-ligands, including simple phosphines and phosphites, as well as bulky biaryl species often employed in catalytic processes. The computed cone angles have been obtained from three different transition metal coordination environments: linear [AuCl(P)] (θL), tetrahedral [Ni(CO)3(P)] (θT) and octahedral [IrCl3(CO)2(P)] (θO), allowing us to observe the steric behavior of the ligand when increasing the steric hindrance around the metal center. The computed cone angles have been extracted from the lowest-energy conformer geometry obtained with a combined MM/DFT methodology.

Benchmarking Density Functional Methods for Calculation of State Energies of First Row Spin-Crossover Molecules.

A systematic study of the performance of several density functional methodologies to study spin-crossover (SCO) on first row transition metal complexes is reported. All functionals have been tested against several mononuclear systems containing first row transition metal complexes and exhibiting spin-crossover. Among the tested functionals, the hybrid meta-GGA functional TPSSh with a triple-ζ basis set including polarization functions on all atoms provides the best results across different metals and oxidation states, and its performance in both predicting the correct ground state and the right energy window for SCO to occur is quite satisfactory.

An Unprecedented Stimuli-Controlled Single-Crystal Reversible Phase Transition of a Metal-Organic Framework and Its Application to a Novel Method of Guest Encapsulation.

The flexibility and unexpected dynamic behavior of a third-generation metal-organic framework are described for the first time. The synthetic strategy is based on the flexibility and spherical shape of dipyridyl-based carborane linkers that act as pillars between rigid Co/BTB (BTB: 1,3,5-benzenetricarboxylate) layers, providing a 3D porous structure (1). A phase transition of the solid can be induced to generate a new, nonporous 2D structure (2) without any loss of the carborane linkers.

Solvation-Guided Design of Fluorescent Probes for Discrimination of Amyloids.

The deposition of insoluble protein aggregates in the brain is a hallmark of many neurodegenerative diseases. While their exact role in neurodegeneration remains unclear, the presence of these amyloid deposits often precedes clinical symptoms. As a result, recent progress in imaging methods that utilize amyloid-specific small molecule probes have become a promising avenue for antemortem disease diagnosis.

Electronic and Steric Control of the Spin-Crossover Behavior in [(Cp)Mn] Manganocenes.

A computational study of the spin-crossover behavior in the family [(Cp)Mn] (R = Me, Pr, Bu) 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) behavior are presented in terms of the cyclopentadienyl (Cp) ligand functionalization. Our calculations outlined a delicate balance between both electronic and steric effects.

Mercurophilic interactions: a theoretical study on the importance of ligands.

In this work, a theoretical analysis of intermolecular HgHg contacts in the presence of different ligands is presented. A survey of structural databases to explore the geometrical preferences among experimental structures presenting short Hg(ii)Hg(ii) contacts reveals the main interaction topologies depending on the nature of the ligand. A benchmark study of several dispersion corrected-density functional methods is carried out to determine the optimal computational methodology for the theoretical study of such interaction.

Structure of the Reduced Copper Active Site in Preprocessed Galactose Oxidase: Ligand Tuning for One-Electron O Activation in Cofactor Biogenesis.

Galactose oxidase (GO) is a copper-dependent enzyme that accomplishes 2e substrate oxidation by pairing a single copper with an unusual cysteinylated tyrosine (Cys-Tyr) redox cofactor. Previous studies have demonstrated that the post-translational biogenesis of Cys-Tyr is copper- and O-dependent, resulting in a self-processing enzyme system. To investigate the mechanism of cofactor biogenesis in GO, the active-site structure of Cu(I)-loaded GO was determined using X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy, and density-functional theory (DFT) calculations were performed on this model.

Electronic Structure Modulation in an Exceptionally Stable Non-Heme Nitrosyl Iron(II) Spin-Crossover Complex.

The highly stable nitrosyl iron(II) mononuclear complex [Fe(bztpen)(NO)](PF6 )2 (bztpen=N-benzyl-N,N',N'-tris(2-pyridylmethyl)ethylenediamine) displays an S=1/2↔S=3/2 spin crossover (SCO) behavior (T1/2 =370 K, ΔH=12.48 kJ mol(-1) , ΔS=33 J K(-1)  mol(-1) ) stemming from strong magnetic coupling between the NO radical (S=1/2) and thermally interconverted (S=0↔S=2) ferrous spin states. The crystal structure of this robust complex has been investigated in the temperature range 120-420 K affording a detailed picture of how the electronic distribution of the t2g -eg orbitals modulates the structure of the {FeNO}(7) bond, providing valuable magneto-structural and spectroscopic correlations and DFT analysis.

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

A diplatinum(II) complex was prepared from a new 1,2-dithienylethene-based ligand containing N-methylimidazole groups as metal-binding units. Reaction of the ligand 1,2-bis[2-methyl-5-(1-methyl-1H-imidazol-2-yl)-3-thienyl]-cyclopentene (L2(H)) with cis-dichlorobis(dimethylsulfoxido)platinum(II) generated the bimetallic complex trans-[Pt2Cl4(DMSO)2(L2(H))] (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 IC50 values in the micromolar range.

Molecular Mechanisms of Spin Crossover in the {Fe(pz)[Pt(CN)4]} Metal-Organic Framework upon Water Adsorption.

The rational design of multifunctional materials with properties that can be selectively controlled at the molecular level is key to the development and application of nanoscale devices. In this study, molecular dynamics simulations using ligand-field molecular mechanics are performed to elucidate, for the first time, the molecular mechanisms responsible for the variation of the spin-crossover properties of the {Fe(pz)[Pt(CN)4]} metal-organic framework upon water adsorption. The simulations demonstrate a direct relationship between the water loading adsorbed in the pores and the variation of the spin-crossover transition temperature, with the high-spin state of the material becoming gradually more stabilized as the number of adsorbed water molecules increases.

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 Fe(II) transition-metal complexes of generic formula [PhB(MesIm)3FeNPR1R2R3]. 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.

Theoretical modeling of spin crossover in metal-organic frameworks: [Fe(pz)2Pt(CN)4] as a case study.

Metal-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 T1/2, 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.