			Home About us Contact

Spin Transition (spin + transition)

Distribution by Scientific Domains

Chemistry	88%

Distribution within Chemistry

General & Introductory Chemistry	46%
Crystallography	12%

Selected Abstracts

Two New Iron(II) Spin-Crossover Complexes with N4O2 Coordination Sphere and Spin Transition around Room Temperature

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 36 2009
Birgit Weber
Abstract The reaction of iron(II) acetate with the tetradentate Schiff base like ligand H2L1 {[3,3,]-[4,5-dihydroxy-1,2-phenylenebis(iminomethylidyne)bis(2,4-pentanedion)]} leads to the formation of the complex [FeL1(MeOH)]. Reaction of this complex with pyridine (py) or N,N,-dimethylaminopyridine (dmap) leads to the two N4O2 -coordinated complexes [FeL1(py)2]·py (1) and [FeL1(dmap)2]·MeOH·0.5dmap (2). Both complexes are spin-crossover compounds that were characterised by using magnetic measurements, X-ray crystallography and temperature-dependent 1H NMR spectroscopy. Special attention was given to the role of the two hydroxy groups on the phenyl ring in the formation of a hydrogen-bonding network and the influence of this network on the spin-transition properties. Although only a gradual spin crossover was observed for both complexes, the transition temperature was shifted to higher temperatures relative to that of the complexes with no additional hydroxy groups at the Schiff base like ligand. The hydrogen-bonding network was responsible for this effect.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Magnetic, 57Fe Mössbauer, and IR Monitoring of the Thermal Spin Transition in a New Family of Iron(II) Spin-Transition Complexes

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2003
Arno F. Stassen
Abstract A new family of iron(II) tetrafluoroborate and perchlorate spin-crossover compounds has been synthesised and is discussed. The iron(II) ion is surrounded by six 1-ethyltetrazole ligands, which are halogen-substituted on the C2 atom of the ethyl group. The spin-crossover temperatures T1/2 are high compared to the unsubstituted (1-alkyltetrazole)iron(II) complexes. The shape of the spin-transition curve (i.e. ,HS vs. T) varies largely over the different complexes and appears to be influenced neither by the crystal packing, nor by the electronic effects. The temperature-dependent spin-transition behaviour has been studied by magnetic susceptibility and by 57Fe-Mössbauer spectroscopy. These data have been supported by temperature-dependent mid-range infrared spectroscopy: the thermally induced spin transition has been observed by direct monitoring of the aromatic C,H stretching frequency. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

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

ADVANCED FUNCTIONAL MATERIALS, Issue 11 2003
A. Bhattacharjee
Abstract 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 Mössbauer spectra and by differential scanning calorimetry (DSC) studies. [source]

An Unprecedented Charge Transfer Induced Spin Transition in an Fe,Os Cluster,

ANGEWANDTE CHEMIE, Issue 8 2010
Matthew
Immer im Kreis herum: Der neuartige Komplex {[Fe(tmphen)2]3[Os(CN)6]2} (siehe Struktur) ist der erste Cluster, in dem sich ein High-Spin-FeIII -Ion in einer Koordinationsumgebung von vier Imin-Stickstoffdonoren und zwei N-koordinierten Cyaniden befindet. Magnetische Messungen offenbaren einen beispiellosen reversiblen ladungstransferinduzierten Spinübergang (CTIST) zwischen Low-Spin-FeII -NC-OsIII und High-Spin-FeIII -NC-OsII. [source]

Unconventional Spin Crossover in Dinuclear and Trinuclear Iron(III) Complexes with Cyanido and Metallacyanido Bridges

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2009
alitro
Abstract A nonsymmetrical triamine, 1,6-diamino-4-azahexane, was Schiff-condensed with (X-substituted) o -salicylaldehyde to yield pentadentate ligands X-L5: salpet and MeBu-salpet. These ligands form mononuclear, dinuclear, and trinuclear FeIII complexes, whose structures were determined by single-crystal X-ray analysis. Of the mononuclear complexes, [FeIII(salpet)Cl] and [FeIII(MeBu-salpet)Cl] are high spin (S = 5/2), whereas [FeIII(salpet)CN]·MeOH is low spin (S = 1/2). The dinuclear and trinuclear complexes show a kind ofthermally induced spin crossover. The dinuclear complex [L5FeIII(CN)FeIIIL5](ClO4)·2H2O (L5 = salpet) is a mixed-spin assembly: the C -coordinated FeIII center is low spin (L) and the N -coordinated FeIII center is high spin (H) at low temperature; an antiferromagnetic interaction occurs between them. This LH reference state is mixed with the LL one. Upon heating, the system shows an increasing content of the HH state. Also, the dinuclear complex [L5FeIII(CN)FeIIIL5](BPh4)·2MeCN (L5 = MeBu-salpet) exhibits a spin transition between LH and HH spin pairs. The mixed-valence trinuclear complex [L5FeIII{FeII(CN)5(NO)}FeIIIL5]·0.5MeOH·3.75H2O (L5 = salpet) shows spin crossover with a residual high-spin fraction at liquid He temperature owing to the LL + LH ground state. The metallacyanido-bridged complex [L5FeIII{Ni(CN)4}FeIIIL5]·2MeOH (L5 = MeBu-salpet) contains a high-spin pair, HH, over the whole temperature interval with a ferromagnetic exchange interaction. A theoretical model was outlined that allows simultaneous fitting of all available experimental data (magnetic susceptibility, magnetization, high-spin mole fraction obtained from the Mössbauer spectra) on a common set of parameters. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Magnetic, 57Fe Mössbauer, and IR Monitoring of the Thermal Spin Transition in a New Family of Iron(II) Spin-Transition Complexes

X-ray structure study of the light-induced metastable states of the spin-crossover compound [Fe(mtz)6](BF4)2

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2001
Joachim Kusz
Iron(II) complexes exhibiting thermal spin-crossover may be converted from the 1A1 low-spin (LS) state to the 5T2 high-spin (HS) state by irradiation with green light (light-induced excited spin-state trapping, LIESST) and from the LS to the HS state by irradiation with red light (reverse LIESST). The lifetime of the metastable LIESST states may be sufficiently long to enable an X-ray diffraction study. The lattice parameters of a single crystal of [Fe(mtz)6](BF4)2 (mtz = methyltetrazole) (space group P21/n) were measured between 300 and 10,K. While one Fe lattice site (A) of the crystal changes from the HS to the LS state near 78,K, the other site (B) remains in the LS state. Using the green light (514,nm) of an argon ion laser the crystal was quantitatively converted to the HS state at 10,K. Irradiation of the crystal at 10,K by red light of a laser diode (820,nm) with site A in the LS and site B in the HS state converts site B almost completely to the LS state. The lattice parameters of both metastable states were measured up to 50,K, where they start to decay on a minute timescale. At 10,K, a full data set for evaluation of the crystal structure was recorded. The volume change of the crystal per complex molecule accompanying the spin transition is 31.5,Å3 at site A and close to zero [,0.21,(14),Å3] at site B. [source]

X-ray emission spectroscopy with a laser-heated diamond anvil cell: a new experimental probe of the spin state of iron in the Earth's interior

JOURNAL OF SYNCHROTRON RADIATION, Issue 5 2005
Jung-Fu Lin
Synchrotron-based X-ray emission spectroscopy (XES) is well suited to probing the local electronic structure of 3d transition metals such as Fe and Mn in their host phases. The laser-heated diamond anvil cell technique is uniquely capable of generating ultra-high static pressures and temperatures in excess of 100,GPa and 3000,K. Here X-ray emission spectroscopy and X-ray diffraction have been interfaced with the laser-heated diamond cell for studying the electronic spin states of iron in magnesiowüstite-(Mg0.75,Fe0.25)O and its crystal structure under lower-mantle conditions. X-ray emission spectra of the ferrous iron in a single crystal of magnesiowüstite-(Mg0.75,Fe0.25)O indicate that a high-spin to low-spin transition of ferrous iron occurs at 54 to 67,GPa and 300,K and the ferrous iron remains in the high-spin state up to 47,GPa and 1300,K. This pilot study points to the unique capability of the synchrotron-based XES and X-ray diffraction techniques for addressing the issue of electronic spin transition or crossover in 3d transition metals and compounds under extreme high- P,T conditions. [source]

Pressure induced high spin to low spin transition in magnesiowüstite

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2006
Taku Tsuchiya
Abstract Using a rotationally invariant formulation of LDA + U, we report a successful study of the high spin (HS)/low spin (LS) transition in low solute concentration magnesiowüstite (Mw), (Mg1,xFex )O, (x < 20%), the second most abundant phase in Earth's lower mantle. The HS state crosses over smoothly to the LS state passing through an insulating mixed spins state where properties change continuously, as seen experimentally. These encouraging results indicate this method should enable first principles studies of strongly correlated iron-bearing minerals, a major class of mineral physics problems. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Nanoparticles of [Fe(NH2 -trz)3]Br2,3,H2O (NH2 -trz=2-Amino-1,2,4-triazole) Prepared by the Reverse Micelle Technique: Influence of Particle and Coherent Domain Sizes on Spin-Crossover Properties

CHEMISTRY - A EUROPEAN JOURNAL, Issue 25 2009
Thibaut Forestier Dr.
Abstract By changing the surfactant/water ratio, nanoparticles of the iron(II) spin crossover material, [Fe(NH2 -trz)3]Br2,3,H2O (with NH2 -trz=4-amino-1,2,4-triazole), have been synthesised from 1,,m down to 30,nm (see figure). Magnetic and reflectivity experiments indicate that the critical size for observing a thermal hysteresis in this 1D polymer family is around 50,nm, and powder X-ray diffraction shows that particles of about 30,nm are constituted by about one coherent domain. This paper describes the synthesis of iron(II) spin-crossover nanoparticles prepared by the reverse micelle technique by using the non-ionic surfactant Lauropal (Ifralan D0205) from the polyoxyethylenic family. By changing the surfactant/water ratio, the size of the particles of [Fe(NH2 -trz)3]Br2,3H2O (with NH2trz=4-amino-1,2,4-triazole) can be controlled. On the macroscopic scale this complex exhibits cooperative thermal spin crossovers at 305 and 320,K. We find that when the size is reduced down to 50,nm, the spin transition becomes gradual and no hysteresis can be detected. For our data it seems that the critical size, for which the existence of a thermal hysteresis can be detected, is around 50,nm. Interestingly, the change of the particle size induces almost no change in the temperature of the thermal spin transition. A systematic determination of coherent domain size carried out on the nanoparticles by powder X-ray diffraction indicates that at approximately 30,nm individual particles consist of one coherent domain. [source]

Interplay Between Kinetically Slow Thermal Spin-Crossover and Metastable High-Spin State Relaxation in an Iron(II) Complex with Similar T1/2 and T(LIESST)

CHEMISTRY - A EUROPEAN JOURNAL, Issue 19 2007
Victoria
Abstract This paper describes the first material to show the well-known light-induced excited spin-state trapping (LIESST) effect, the metastable excited state of which relaxes at a temperature approaching its thermal spin-crossover. Cooling polycrystalline [FeL2][BF4]2,x,H2O (L=2,6-bis{3-methylpyrazol-1-yl}pyridine; x=0,1/3) at 1,K,min,1 leads to a cooperative spin transition, taking place in two steps centered at 147 and 105,K, that is only 54,% complete by magnetic susceptibility. Annealing the sample at 100,K for 2,h results in a slow decrease in ,MT to zero, showing that the remainder of the spin-crossover can proceed, but is kinetically slow. The crystalline high- and fully low-spin phases of [FeL2][BF4]2,x,H2O are isostructural (C2/c, Z=8), but the spin-crossover proceeds via a mixed-spin intermediate phase that has a triple unit cell (C2/c, Z=24). The water content of the crystals is slowly lost on exposure to air without causing decomposition. However, the high-spin/mixed-spin transition in the crystal proceeds at 110±20,K when x=1/3 and 155±5,K when x=0, which correspond to the two spin-crossover steps seen in the bulk material. The high-spin state of the compound is generated quantitatively by irradiation of the low-spin or the mixed-spin phase at 10,K, and in approximately 70,% yield by rapidly quenching the sample to 10,K. This metastable high-spin state relaxes back to the low-spin ground state at 87±1,K in one, not two, steps, and without passing through the intermediate phase. This implies that thermal spin-crossover and thermally activated high-spin,low-spin relaxation in this material become decoupled, thus avoiding the physical impossibility of T(LIESST) being greater than T1/2. [source]

Solid- and Solution-State Studies of the Novel ,-Dicyanamide-Bridged Dinuclear Spin-Crossover System {[(Fe(bztpen)]2[,-N(CN)2]}(PF6)3,n,H2O,

CHEMISTRY - A EUROPEAN JOURNAL, Issue 19 2005
Norma Ortega-Villar
Abstract The mononuclear diamagnetic compound {Fe(bztpen)[N(CN)2]}(PF6)CH3OH (1) (bztpen = N -benzyl- N,N,,N,-tris(2-pyridylmethyl)ethylenediamine) has been synthesized and its crystal structure studied. Complex 1 can be considered to be the formal precursor of two new dinuclear, dicyanamide-bridged iron(II) complexes with the generic formula {[(Fe(bztpen)]2[,-N(CN)2]}(PF6)3,n,H2O (n = 1 (2) or 0 (3)), which have been characterized in the solid state and in solution. In all three complexes, the iron atoms have a distorted [FeN6] octahedral coordination defined by a bztpen ligand and a terminal (1) or a bridging dicyanamide ligand (2 and 3). In the solid state, 2 and 3 can be considered to be molecular isomers that differ by the relative position of the phenyl ring of the two {Fe(bztpen)[N(CN)2]}+ halves (cis and trans, respectively). Depending on the texture of the sample, 2 exhibits paramagnetic behavior or displays a very incomplete spin transition at atmospheric pressure. Complex 3 undergoes a gradual two-step spin transition with no observed hysteresis in the solid state. Both steps are approximately 100 K wide, centered at ,200 K and ,350 K, with a plateau of approximately 80 K separating the transitions. The crystal structure of 3 has been determined in steps of approximately 50 K between 400 K and 90 K, which provides a fascinating insight into the structural behavior of the complex and the nature of the spin transition. Order,disorder transitions occur in the dicyanamide bridge and the PF6, ions simultaneously, with the spin-crossover behavior suggesting that these transitions may trigger the two-step character. In solution, 2 and 3 display very similar continuous spin conversions. Electrochemical studies of 2 and 3 show that the voltammograms are typical of dimeric systems with electronic coupling of the metals through the dicyanamide ligand. [source]

Spin-Crossover Physical Gels: A Quick Thermoreversible Response Assisted by Dynamic Self-Organization

CHEMISTRY - AN ASIAN JOURNAL, Issue 1 2007
Tsuyohiko Fujigaya
Abstract Iron(II) triazolate coordination polymers with lipophilic sulfonate counterions with alkyl chains of different lengths have been synthesized. In hydrocarbon solvents, these polymers formed a physical gel and showed a thermoreversible spin transition upon the sol,gel phase transition. The formation of a hydrogen-bonding network between the triazolate moieties and sulfonate ions, bridged by water molecules, was found to play an important role in the spin-crossover event. The spin-transition temperature was tuned over a wide range by adding a small amount of 1-octanol, a scavenger for hydrogen-bonding interactions. This additive was essential for the iron(II) species to adopt a low-spin state. Compared with nongelling references in aromatic solvents, the spin-crossover physical gels are characterized by their quick thermal response, which is due to a rapid restoration of the hydrogen-bonding network, possibly because of a dynamic structural ordering through an enhanced lipophilic interaction of the self-assembling components in hydrocarbon solvents. [source]

Optical, Magnetic and Structural Properties of the Spin-Crossover Complex [Fe(btr)2(NCS)2]·H2O in the Light-Induced and Thermally Quenched Metastable States

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 36 2007
Vincent Legrand
Abstract [Fe(btr)2(NCS)2]·H2O [btr = 4,4,-bis(1,2,4-triazole)] is thearchetype of highly cooperative and low-dimensional spin-crossover complexes, which exhibit low-spin (LS) to high-spin (HS) light-induced conversion at very low temperature. The structural reorganizations related to the light-induced and thermally induced LS,HS transitions were characterized by single-crystal X-ray diffraction below the relaxation temperature (T = 15 K < TLIESST) and at 130 K within the thermal hysteresis loop. We show that the LIESST and thermal spin transitions lead to the same structural variations, namely an elongation of the Fe,N bonds by 0.18 Å (Fe,NNCS) and 0.20 Å (Fe,Nbtr), on going from LS to HS, together with a reorientation of the NCS group by nearly 13°. The atomic displacement amplitudes, derived from the crystal structures, indicate lattice vibration modes of larger amplitudes and correlatively lower vibration frequencies in the HS state. The deformation of the crystal lattice as a function of temperature and laser excitation was quantitatively analyzed in terms of the HS and LS thermal-expansion (,HS and ,LS) and spin-transition spontaneous-strain (,) tensors. The eigendirections and eigenvalues of the , and , tensors correlate well with the weak and strong interactions in the solid and are responsible for the high cooperativity and low-dimensional behaviour. Magnetic and spectroscopic measurements were performed in all the different spin states and related to the structural findings. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Pressure Effect Investigations on the Spin Crossover Systems{Fe[H2B(pz)2]2(bipy)} and {Fe[H2B(pz)2]2(phen)}

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2006
Ana Galet
Abstract Pressure effect studies on the spin crossover behaviour of the mononuclear compounds {Fe[H2B(pz)2]2(bipy)}(1) and {Fe[H2B(pz)2]2(phen)}(2) have been performed in the range of 105 Pa,1.02 GPa at variable temperatures (100,310 K). Continuous spin transitions and displacement of its characteristic temperature has been observed for 1 with increasing pressure. Meanwhile the response of 2 under applied pressures is quite unexpected, and can only be understood in terms of a crystallographic phase transition or change in the bulk modulus of the compound. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]