Search results for "STATES"

Understanding the reactivity of transition metal complexes involving multiple spin states

2003

International audience; In coordination chemistry, many reactions involve several electronic states, in particular states of different spin. This phenomenon of ‘Multiple-State Reactivity’ has been recognized for some time, both for gas-phase reactions of ‘bare’ metal ions, and for transition metal complexes in solution. Until recently, however, much of the discussion of these systems has remained qualitative, because standard computational methods do not allow the location of the critical points for these processes, the Minimum Energy Crossing Points (MECPs) between states of different spin. Increased computational resources and new algorithms now enable MECPs to be located for large, reali…

Mössbauer investigation of the photoexcited spin states and crystal structure analysis of the spin-crossover dinuclear complex [{Fe(bt)(NCS)(2)}(2)bp…

2006

The crystal structure of the complex [{Fe(bt)(NCS)(2)}(2)bpym] (1) (bt=2,2'-bithiazoline, bpym=2,2'-bipyrimidine) has been solved at 293, 240, 175 and 30 K. At all four temperatures the crystal remains in the P space group with a=8.7601(17), b=9.450(2), c=12.089(3) A, alpha=72.77(2), beta=79.150(19), gamma=66.392(18) degrees , V=873.1(4) Angstrom(3) (data for 293 K structure). The structure consists of centrosymmetric dinuclear units in which each iron(II) atom is coordinated by two NCS(-) ions in the cis position and two nitrogen atoms of the bridging bpym ligand, with the remaining positions occupied by the peripheral bt ligand. The iron atom is in a severely distorted octahedral FeN(6) e…

Spin-crossover nanoparticles anchored on MoS2 layers for heterostructures with tunable strain driven by thermal or light-induced spin switching

2021

In the past few years, the effect of strain on the optical and electronic properties of MoS2 layers has attracted particular attention as it can improve the performance of optoelectronic and spintronic devices. Although several approaches have been explored, strain is typically externally applied on the two-dimensional material. In this work, we describe the preparation of a reversible ‘self-strainable’ system in which the strain is generated at the molecular level by one component of a MoS2-based composite material. Spin-crossover nanoparticles were covalently grafted onto functionalized layers of semiconducting MoS2 to form a hybrid heterostructure. Their ability to switch between two spi…

ChemInform Abstract: Spin Crossover, LIESST, and NIESST-Fascinating Electronic Games in Iron Complexes

2010

Abstract Coordination compounds of transition metal ions with open-shell electron configurations may exhibit dynamic electronic structure phenomena depending on the nature of the coordinating ligand sphere. The change of spin state with temperature (thermal spin crossover”) and light-induced electron transfer processes leading to long-lived metastable states are among the most fascinating electronic games encountered in transition metal compounds and are presently under intensive study by chemists and physicists. The first part of this lecture will survey briefly some highlights of previous work and present recent results on thermal spin crossover in iron(II) compounds. The second part of t…

The photocycle and the structure of iron containing bacteriorhodopsin ?a kinetic and M�ssbauer spectroscopy investigation

1990

Bacteriorhodopsin (bR), converted by deionization to the blue form was reconstituted to the active purple membrane by the addition of Fe2+ or Fe3+ ions. 57Fe Mossbauer spectra of these samples were measured at different pH values (pH 3.9, pH 5.0 and pH 7.0) and at temperatures ranging from 4 K to 300 K. The hyperfine parameters reveal two iron environments with oxygen atoms in the neighbourhood of iron. Iron type 1 is in the 3+ high spin state. It is bound to acid side chains of the protein and/or the phosphate groups of the lipids. Iron type 2 is in the 2+ high spin state and is linked to carboxy groups of the protein in a rather unspecific way. Dynamics as measured by Mossbauer spectrosco…

Experimental Realization of a Dirac Monopole through the Decay of an Isolated Monopole

2017

We experimentally observe the decay dynamics of deterministically created isolated monopoles in spin-1 Bose-Einstein condensates. As the condensate undergoes a change between magnetic phases, the isolated monopole gradually evolves into a spin configuration hosting a Dirac monopole in its synthetic magnetic field. We characterize in detail the Dirac monopole by measuring the particle densities of the spin states projected along different quantization axes. Importantly, we observe the spontaneous emergence of nodal lines in the condensate density that accompany the Dirac monopole. We also demonstrate that the monopole decay accelerates in weaker magnetic field gradients.

Electric field control of the spin state in mixed-valence magnetic molecules.

2012

Multiferroic molecules for spintronics: In a many-electron mixed-valence dimer with dominant double exchange, as compared with antiferromagnetic superexchange, the electric field is shown to induce a spin crossover from the ferromagnetic spin state to the antiferromagnetic one. This leads to a sharp decrease in the magnetic moment of the molecule and a simultaneous stepwise increase in the electric dipole (see figure).

MR2666967 Jäkel, Christian D.; Narnhofer, Heide; Wreszinski, Walter F. On the mixing property for a class of states of relativistic quantum fields. J…

2011

First-order interface localization-delocalization transition in thin Ising films using Wang-Landau sampling

2004

Using extensive Monte Carlo simulations, we study the interface localization- delocalization transition of a thin Ising film with antisymmetric competing walls for a set of parameters where the transition is strongly first-order. This is achieved by estimating the density of states (DOS) of the model by means of Wang-Landau sampling (WLS) in the space of energy, using both, single-spin-flip as well as N-fold way updates. From the DOS we calculate canonical averages related to the configurational energy, like the internal energy, the specific heat, as well as the free energy and the entropy. By sampling microcanonical averages during simulations we also compute thermodynamic quantities relat…

Vector coherent states and intertwining operators

2009

In this paper we discuss a general strategy to construct vector coherent states of the Gazeau-Klauder type and we use them to built up examples of isospectral hamiltonians. For that we use a general strategy recently proposed by the author and which extends well known facts on intertwining operators. We also discuss the possibility of constructing non-isospectral hamiltonians with related eigenstates.