Search results for "crossover"
showing 10 items of 658 documents
Pressure effect studies on spin crossover systems
2005
Abstract In the present review article we discuss the results of investigations of the influence of hydrostatic pressure (up to 1.2 GPa) on the spin transition behaviour in coordination compounds of 3d transition metal ions. The systems under investigation are mononuclear spin crossover compounds of iron(II) and chromium(II), dinuclear complexes of iron(II) exhibiting coexistence of intramolecular anti-ferromagnetic coupling and thermal spin crossover, and 1D, 2D and 3D polynuclear spin crossover complexes of iron(II). It is demonstrated that the application of hydrostatic pressure serves as a tool for modifying the ligand field strength in a controlled manner.
Phase Trapping in Multistep Spin Crossover Compound
2020
The dimeric motif is the smallest unit for two interacting spin centers allowing for systematic investigations of cooperative interactions. As spin transition compounds, dinuclear complexes are of particular interest, since they potentially reveal a two-step spin crossover (SCO), switching between the high spin-high spin [HS-HS], the high spin-low spin [HS-LS], and the low spin-low spin [LS-LS] states. Herein, we report the synthesis and characterization of six dinuclear iron(II) complexes [FeII2(μ2-L1)2](BF4)4 (C1), [FeII2(μ2-L1)2](ClO4)4 (C2), [FeII2(μ2-L1)2](F3CSO3)4 (C3), [FeII2(μ2-L2)2](BF4)4 (C4), [FeII2(μ2-L2)2](BF4)4 (C5), and [FeII2(μ2-L2)2](BF4)4 (C6), based on the 1,3,4-thiadiazo…
Spin-crossover iron(ii) complex showing thermal hysteresis around room temperature with symmetry breaking and an unusually high T(LIESST) of 120 K.
2019
We report a Fe(II) complex based on 4′,4′′ carboxylic acid disubstituted dipyrazolylpyridine that shows a spin-crossover close to room temperature associated to a crystallographic phase transition and the LIESST effect with a high T(LIESST) of 120 K.
Spin crossover in soft matter
2014
Abstract This review article is devoted to the study of the spin crossover phenomenon in soft matter. Spin crossover compounds, though known for decades, bear the potential for practical applications in switching, sensing and display devices. Having arrived at a reasonable understanding of the spin transition process in solid and liquid states, one trend in this research field is to extend the knowledge into soft matter. The review begins with a brief description of Langmuir–Blodgett thin films based on FeII coordination compounds since it represents the first study of the spin crossover phenomenon in soft matter. The following section illustrates the FeII, FeIII and CoII complexes reported…
The intermediate coherent scattering function of entangled polymer melts: a Monte Carlo test of des Cloizeaux' theory
1994
Using the bond fluctuation model for flexible polymer chains in a dense melt the intermediate coherent scattering function for chains containing N=200 monomers is calculated and interpreted in terms of a recent theory of des Cloizeaux. The theory yields an explicit description for the crossover from the Rouse model to the regime where reptation prevails, for the limit N→∞. While the Monte Carlo data are qualitatively compatible with this description, an accurate estimation of the tube diameter is prevented due to the onset of a diffusive decay of the scattering function, not included in the theory. For a full quantitative analysis of the Monte Carlo data (as well as of experiments on chains…
Dynamical Scaling in Polymer Solutions Investigated by the Neutron Spin-Echo Technique
1979
Chain dynamics in polymer solutions was investigated by means of the recently developed neutron spin echo spectroscopy. — By this technique, it was possible for the first time to verify unambiguously the scaling predictions of the Zimm model in the case of single chain behaviour and to observe the cross over to many chain behaviour. The segmental diffusion of single chains exhibits deviations from a simple exponential law, indicating the importance of memory effects. Mit Hilfe der erst kurzlich entwickelten Neutronen-Spin-Echo-Spektroskopie wurde die Kettendynamik von Polymermolekulen im gelosten Zustand untersucht. - Die Methode eroffnete die Moglichkeit, zum ersten Mal fur das Einzelkette…
GPU Based Molecular Dynamics Simulations of Polymer Rings in Concentrated Solution: Structure and Scaling
2011
We report on equilibrium properties of a concentrated solution of non-concatenated ring polymers by Molecular dynamics simulations using HooMD-blue, a fast implementation on graphics processor units (GPUs). We are able to identify the intermediate scaling regime for the radius of gyration Rg ∝ N as well as indication for a crossover to Rg ∝ N for rings with chain length N in our fully flexible off-lattice polymer model. This crossover takes place between a ring size of 2500 and 7500 monomers for monomer density ρ = 0.5. Our results are in agreement with recent studies for lattice and stiff off-lattice models and show once again that this scaling is not model dependent at all. Furthermore th…
Adsorption Transition of a Polymer Chain at a Weakly Attractive Surface: Monte Carlo Simulation of Off-Lattice Models
2002
A bead-spring model of a polymer chain with one end attached to a wall is studied by Monte Carlo simulations for chain lengths 16 ≤ N ≤ 256. Two types of adsorption potentials, 9-3 and 10-4 Lennard-Jones (LJ) potentials, between the effective monomers and the wall are assumed. For both cases the adsorption transition where the chain changes its asymptotic statistical properties from a three-dimensional to a two-dimensional configuration is located using a scaling analysis. It is shown that the crossover exponent φ = 0.50 ± 0.02 is the same for both LJ potentials. This value is compatible with recent theoretical predictions and simulation results for lattice models with short-range wall pote…
A Mixed-Ligand Approach for Spin-Crossover Modulation in a Linear FeII Coordination Polymer
2014
In this work, we present a family of Fe(II) coordination polymers of general formula [Fe(btzx)(3-3x)(btix)(3x)](ClO4)2 with interesting spin-crossover properties. These coordination polymers have been synthesized using chemical mixtures of two different but closely related ligands, 1,4-bis(tetrazol-1-ylmethyl)benzene (btzx) and 1,4-bis(triazol-1-ylmethyl)benzene (btix), and the effect of a gradual substitution of the ligand in the spin transition temperature has been investigated. Several chemical mixtures have been structurally characterized by X-ray powder diffraction indicating a clear critical amount in the composition of the mixture after which mixed phases rather than a single phase c…
Photoswitchable coordination compounds
2001
Photoswitchable compounds represent an attractive class of materials in coordination chemistry. Recent progress dealing with transition metal compounds involving photo-induced changes of the magnetic and/or optical properties to long-lived metastable states are covered in the present review article. The basic photophysical phenomena together with representative examples such as nitroprusside derivatives, relevant spin crossover complexes, stilbenoid complexes and finally Prussian blue analogues are discussed. Some possible applications regarding energy and information storage are suggested at the end.