Search results for "spin state"

LIESST Effect in Fe(II) 1,2,4-Triazole Chains

2016

One-dimensional Fe(II) chains with 1,2,4-triazole as bridging ligands present the LIESST effect; i.e. their spin state switched from low-spin to high-spin after light irradiation at low temperature. This account summarizes the findings in this area of photomagnetism where 57Fe Mossbauer spectroscopy was used as a primary detection tool of the LIESST effect.

Solvent-induced high-spin transition in double-decker 3d–4f metallacrowns

2019

Element-specific magnetic spin and orbital magnetic moments of $3d\text{\ensuremath{-}}4f$ double-decker metallacrown molecules have been investigated using x-ray magnetic circular dichroism. The double-decker metallacrowns comprise one rare-earth Gd(III) or Tb(III) ion embedded between two squared scaffolds of four Ni(II) ions. We observe a strong increase of the Ni(II) moments if the molecules are dissolved in methanol, indicating a spin crossover from a low-spin to a high-spin state. In contrast, dichloromethane does not change the spin state. This result is explained by a change of the coordination environment of nickel. The comparison of charge-transfer multiplet calculations with the …

57Fe- MÖSSBAUER EMISSION SPECTROSCOPY OF AN IRON (II) COMPLEX WITH TEMPERATURE DEPENDENT SPIN STATE

1980

ANOMALOUS SPIN STATES OF IRON (II) IN MÖSSBAUER EMISSION SPECTRA OF [57 Co(2-CH3-phen),] (ClO4)2.2 H2O AND [57Co(2-CH3O-phen)3] (ClO4)2.H2O

1976

Spin Crossover Metal-Organic Frameworks with Inserted Photoactive Guests: On the Quest to Control the Spin State by Photoisomerization

2021

International audience; Three Hofmann-like metal-organic frameworks {Fe(bpac)[Pt(CN)4]}•G (bpac=1,2-bis(4-pyridyl)acetylene) were synthesized with photoisomerizable guest molecules (G = trans-azobenzene, trans-stilbene or cis-stilbene) and were characterized by elemental analysis, thermogravimetry and powder X-ray diffraction. The insertion of guest molecules and their conformation were inferred from Raman and FTIR spectra and from single-crystal X-ray diffraction and confronted with computational simulation. The magnetic and photomagnetic behaviors of the framework are significantly altered by the different guest molecules and different conformations. On the other hand, photoisomerization …

Guest Effect on Nanopatterned Spin-Crossover Thin Films

2011

International audience; Nanopatterned thin films of the metal–organic framework {Fe(bpac)[Pt(CN)4]} (bpac=bis(4‐pyridyl)acetylene) are elaborated by the combination of a sequential assembly process and a lithographic method. Raman microspectroscopy is used to probe the temperature dependence of the spin state of the iron(II) ions in the films (40–90 nm in thickness), and reveals an incomplete but cooperative spin transition comparable to that of the bulk material. Adsorption/desorption of pyridine guest molecules is found to have a substantial influence on the spin‐crossover properties of the thin layers. This interplay between host–guest and spin‐crossover properties in thin films and nano…

Hyperpolarization of cis ‐ 15 N 2 ‐Azobenzene by Parahydrogen at Ultralow Magnetic Fields**

2021

The development of nuclear spins hyperpolarization, and the search for molecules that can be efficiently hyperpolarized is an active area in nuclear magnetic resonance. In this work we present a detailed study of SABRE SHEATH (signal amplification by reversible exchange in shield enabled alignment transfer to heteronuclei) experiments on 15 N2 -azobenzene. In SABRE SHEATH experiments the nuclear spins of the target are hyperpolarized through transfer of spin polarization from parahydrogen at ultralow fields during a reversible chemical process. Azobenzene exists in two isomers, trans and cis. We show that all nuclear spins in cis-azobenzene can be efficiently hyperpolarized by SABRE at suit…

Anomalous Spin Transition Observed in Bis(2,6-bis(pyrazol-3-yl)pyridine)iron(II) Thiocyanate Dihydrate

2003

Bis(2,6-bis(pyrazol-3-yl)pyridine)iron(II) thiocyanate dihydrate undergoes a two-step singlet (1A1) ⇄ quintet (5T2) transition in which both steps are associated with thermal hysteresis. Thermal cycling of the sample results in its conversion to a second phase which displays a single-step transition with a very narrow hysteresis loop. This second phase slowly reverts to the initial phase on standing at 300 K. The interconversions are completely reversible. The spin state changes have been monitored by measurement of magnetism and Mossbauer spectra and by differential scanning calorimetry (DSC) studies.

Smart molecular/MoS2 Heterostructures Featuring Light and Thermally-Induced Strain Driven by Spin Switching

2020

In this work we exploit the ability of spin-crossover molecules to switch between two spin states, upon the application of external stimuli, to prepare smart molecular/2D heterostructures. Through the chemical design of the hybrid interface, that involves a covalent grafting between the two components, we obtain a hybrid heterostructure formed by spin-crossover nanoparticles anchored on chemically functionalized monolayers of semiconducting MoS2. In the resulting hybrid, the strain generated by the molecular system over the MoS2 layer, as a consequence of a thermal or light-induced spin switching, results in a dramatic and reversible change of its electrical and optical properties. This nov…

Fascinating electronic games in iron complexes

1996

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»), light-induced electron transfer processes leading to long-lived metastable charge and spin states (e.g., «LIESST» effect), are some of the fascinating electronic games encountered in transition metal compounds, which are presently under extensive study by chemists and physicists. Mossbauer spectroscopy plays a dominant role in the investigation of such phenomena in iron compounds, as will be demonstrated in this paper. This wo…