Search results for "LIESST"
showing 10 items of 72 documents
Cooperative effects on the HS→LS relaxation in the [Fe(ptz)6](BF4)2 spin-crossover system
1992
Abstract The high-spin to low-spin (HS→LS) relaxation in the [Fe(ptz) 6 ](BF 4 ) 2 spin-crossover system deviates strongly from first-order kinetics because of cooperative effects of elastic origin. The shift in horizontal and vertical displacement of the potential wells of the initial and final state relative to each other due to the build-up of an “internal” pressure is estimated from spectroscopic measurements. The HS→LS relaxation as such is described by the theory of nonadiabatic multiphonon relaxation in the strong-coupling limit, with a Huang—Rhys factor S ≈ 45 which is much larger than the reduced energy gap p . The sigmoidal relaxation curves in [Fe(ptz) 6 ](BF 4 ) 2 result when a …
Spin crossover phenomena in Fe(ii) complexes
2000
The behaviour of spin crossover compounds is among the most striking and fascinating shown by relatively simple molecular species. This review aims to draw attention to the various ways in which spin crossover phenomena are manifested in iron(II) complexes, to offer some rationalisation for these, and to highlight their possible applications. Typical examples have been selected along with more recent ones in order to give an overall view of the scope and development of the area. The article is structured to provide the basic material for those who wish to enter the field of spin crossover.
Thermal and Light-Induced Spin Transition in [Fe(bpen)X2] (bpen = 1,6-Bis(2-pyridyl)-2,5-diazahexane, X = NCS-, NCSe-)
1996
The thermal and light-induced spin transitions in [Fe(bpen)(NCS)2] and [Fe(bpen)(NCSe)2] have been investigated by means of magnetic susceptibility and Mossbauer measurements. The HS → LS transition in [Fe(bpen)(NCS)2] is detected at temperatures below 120 K (T1/2 [when the fraction of high-spin species γHS = 0.5] = 68 K) with a residual HS fraction of 8% at 20 K. The transition is fairly abrupt and no hysteresis is observed, in contrast to earlier studies (ref. [8]). The generation of metastable HS states in [Fe(bpen)(NCS)2] is achieved by rapid cooling of the sample and by irradiating the compound at low temperatures with light of appropriate wavelengths (LIESST). The HS → LS relaxation o…
Photomagnetism of a Series of Dinuclear Iron(II) Complexes
2009
International audience; The photomagnetic properties of a series of [{Fe(NCS)(py-X)}2(bpypz)2] (NCS=thiocyanate, py=pyridine, X=4-Mepy, py, 3-Mepy, 3-Clpy and 3-Brpy, and bpypz=3,5-bis(pyridine-2-yl)pyazolate) binuclear complexes are close to the antiferromagnetic response of [{Fe(NCS)(3,5-dmpy)}3(bpypz)2] (3,5-dmpy=3,5-dimethylpyrazine), which is characterised by two iron(II) metal ions in a high-spin (HS) electronic configuration . This paper describes the photomagnetic properties of a series of binuclear iron(II) complexes belonging to the [{Fe(NCS)(py-X)}2(bpypz)2] family (NCS=thiocyanate; py=pyridine; bpypz=3,5-bis(pyridine-2-yl)pyrazolate; and py-X=4-Mepy (1), py (3), 3-Mepy (4), 3-Cl…
Fe(II) spin crossover complexes of a derivative of 2,6-bis(pyrazol-1-yl)pyridine (1-bpp) functionalized with a carboxylic acid in the 3-pyridyl posit…
2019
Abstract The preparation of a new bis(pyrazol-1-yl)pyridine (1-bpp) derivative functionalized with a carboxylic acid in the 3-pyridyl position, bpp3-COOH ligand is reported together with the structure and spin-crossover (SCO) properties of [FeII(bpp3-COOH)2](ClO4)2·0.5EtOH·0.5H2O (1). Magnetic properties of 1 indicate that LS is favored. Desolvation leads to a gradual and incomplete SCO. Solvated and desolvated compounds show LIESST effect.
Spin-crossover compounds based on iron(II) complexes of 2,6-bis(pyrazol-1-yl)pyridine (bpp) functionalized with carboxylic acid and ethyl carboxylic …
2018
International audience; Four new salts of the iron(II) complex of the 2,6-bis(pyrazol-1-yl)pyridine ligand functionalized with a carboxylic acid group (bppCOOH) of formulas [Fe(bppCOOH)2](BF4)2 (1(BF4)2), [Fe(bppCOOH)2](CF3SO3)2·yMe2CO (1(CF3SO3)2·yMe2CO), [Fe(bppCOOH)2](AsF6)2·yMe2CO (1(AsF6)2·yMe2CO) and [Fe(bppCOOH)2](SbF6)2·yMe2CO (1(SbF6)2·yMe2CO) have been prepared and characterized together with a more complete structural and photomagnetic characterization of the previously reported [Fe(bppCOOH)2](ClO4)2 (1(ClO4)2). Furthermore, the iron(II) complex of the ethyl ester derivative of bppCOOH (bppCOOEt) has been prepared and characterized (compound [Fe(bppCOOEt)2](ClO4)2·yMe2CO, 2(ClO4)…
2D Bimetallic Oxalate‐Based Ferromagnets with Inserted [Fe(4‐Br‐sal 2 ‐trien)] + and [Fe(3‐R‐sal 2 ‐trien)] + (R = Br, Cl and CH 3 O) Fe III Spin‐Cro…
2012
The syntheses, structures and magnetic properties of the compounds of formula [FeIII(4-Br-sal2-trien)][MnIICrIII(ox)3]0.67Cl0.33·CH3OH_solvate (1), [FeIII(3-Br-sal2-trien)][MnIICrIII(ox)3]·(CH3CN)2 (2), [FeIII(3-Cl-sal2-trien)][MnIICrIII(ox)3]·(CH3OH)2·(CH3CN)2 (3) and [FeIII(3-CH3O-sal2-trien)][MnIICrIII(ox)3]·(CH3OH)·(H2O)1.5·(CH2Cl2)0.5 (4) are reported. The four structures present a 2D honeycomb anionic layer formed by MnII and CrIII ions linked through oxalate ligands and a cationic layer of the FeIII complexes intercalated between the 2D oxalate network. The main differences compared with previous 2D oxalate-based structures are the presence of double layers of cations in compounds 1,…
Spin state switching in iron coordination compounds
2013
The article deals with coordination compounds of iron(II) that may exhibit thermally induced spin transition, known as spin crossover, depending on the nature of the coordinating ligand sphere. Spin transition in such compounds also occurs under pressure and irradiation with light. The spin states involved have different magnetic and optical properties suitable for their detection and characterization. Spin crossover compounds, though known for more than eight decades, have become most attractive in recent years and are extensively studied by chemists and physicists. The switching properties make such materials potential candidates for practical applications in thermal and pressure sensors …
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.
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.