Search results for "spin transition"
showing 10 items of 173 documents
Spin Transition of 1D, 2D and 3D Iron(II) Complex Polymers The Tug-of-War between Elastic Interaction and a Shock-Absorber Effect
2003
The structures of linear chain Fe(II) spin-crossover compounds of α,β- and α,ω-bis (tetrazol-1-yl)alkane type ligands are described in relation to their magnetic properties. The first threefold interlocked 3-D catenane Fe(II) spin-transition system, [μ-tris(1,4-bis(tetrazol-1-yl)butane-N1,N1′) iron(II)] bis(perchlorate), will be discussed. An analysis is made among the structures and the cooperativity of the spin-crossover behaviour of polynuclear Fe(II) spin-transition materials.
Pressure Effect Studies on the Spin Transition of Microporous 3D Polymer [Fe(pz)Pt(CN)4]
2018
Pressure effects on the spin transition of the three-dimensional (3D) porous coordination polymer {Fe(pz)[Pt(CN)4]} have been investigated in the interval 105 Pa–1.0 GPa through variable-temperature (10–320 K) magnetic susceptibility measurements and spectroscopic studies in the visible region at room temperature. These studies have disclosed a different behavior of the compound under pressure. In the magnetic experiments, a temperature independent paramagnetic behavior has been observed under 0.4 GPa. In contrast, at room temperature and at 0.8 GPa, a complete HS-to-LS transition has been evidenced. The differences in the magnetic behavior are strongly related with the porous structure of …
Pressure Effect Studies on the 3D Spin Crossover System: {Fe(3CN-py)2[M(CN)2]2}·nH2O (n < 2/3, M = Ag(I), Au(I))
2007
[EN] Pressure effect investigations on the magnetic behaviour of the 3D SCO polymers {Fe(3CN-py)2[Ag(CN)2]2} · 2/3H2O (1) and {Fe(3CN-py)2[Au(CN)2]2} · 2/3H2O (2) have been carried out in the range of 105 Pa to 0.7 GPa. Despite both compounds are isostructural their magnetic behaviour under applied hydrostatic pressures is very different. Strong nonlinearity in the Tc(P) vs. P plot has been observed for compound 1 a fact which contrasts with the almost linear dependence observed for each spin transition in 2. However, both compounds are extremely sensitive to the application of pressure as well as the Tc(P) vs. P plots denote.
Protein Unfolding:1H-NMR Studies of Paramagnetic Ferricytochrome c-550 from Horse Heart
2005
Electronic transfer protein cytochrome c-550 from horse heart is studied in the unfolded state by means of paramagnetic 1H NMR. The protein contains 104 aminoacid residues and a heme group with low spin FeIII ion in the oxidized form of protein. The global secondary structure is of the α-helix type as occurs in the case of very other cytochromes c investigated such as cyt c-550 from Thiobacillus versutus or cyt c-551 from Pseudomonas aeruginosa. We have studied the coordination characteristic and electronic properties of heme iron horse heart ferricytochrome c-550 at increasing denaturing conditions (up to 3.1 M GuHCl and 288-323 K). The 1H T1 values of the signals were measured and some re…
1H NMR studies of paramagnetic ferricytochrome c-551 from Pseudomonas aeruginosa at high pH: The role of histidine 16 in the spin transition
2005
Abstract Cytochrome c-551 from the mesophile Pseudomonas aeruginosa is an electronic transfer protein that contains 82 amino-acid residues and a c-type heme as the prosthetic group with low spin Fe(II) in the reduced form and low spin Fe(III) in the oxidized form of cytochrome c-551. We have studied the electronic properties of ferricytochrome c-551 from P. aeruginosa at high pH (9–11.4) by means of paramagnetic 1H NMR spectra and the T1 and T2 values of isotropically shifted proton resonances. We have also analyzed the temperature dependence of the hyperfine-shifts. Resonance assignment of some signals was based on 2D saturation transfer experiments, EXSY. These results indicate the existe…
Spin crossover FeII complexes as templates for bimetallic oxalate-based 3D magnets
2007
Abstract We present the synthesis and structural characterization of the salt [Fe(bpp)2][MnCr(ox)3]2 · bpp · CH3OH. It crystallizes in the monoclinic space group. This material contains an anionic [MnCr(ox)3]− 3D 10-gon ferromagnetic network, that orders below 3.0 K. The channels created by this architecture are filled by the spin crossover cations [Fe(bpp)2]2+ (bpp = 2,6(bispyrazol-3-yl)pyridine), free ligand and solvent molecules. No spin transition has been observed at ambient pressure.
Spin transition in three-dimensional bridged coordination polymers of iron(II)–urea-triazoles
2008
Abstract Three-dimensional spin-crossover (SCO) networks of [Fe 2 ( n -Rdubtrz) 3 ](X) 4 · n H 2 O ( n -R = (CH 2 ) y , y = 4, 6, 8, 12; du = diurea; btrz = bis-triazole; X = BF 4 - , ClO 4 - , triflate, tosylate) coordination polymers are prepared by reaction of bridging aliphatic bis-urea triazoles ( n -Rdubtrz) with the iron-salts (FeX 2 ). Investigations of the properties are supported by studies of one-dimensional compounds of [Fe(Rtrzu) 3 ](X) 2 (R = n -propyl, t -butyl; trzu = urea triazole). Characterization of the complexes is carried out with IR-spectroscopy, elemental analysis, TGA and atomic absorption spectroscopy. SCO-behaviour of all complexes is inspected by magnetic sus…
Hofmann-Like Frameworks Fe(2-methylpyrazine)n[M(CN)2]2 (M = Au, Ag) : Spin-Crossover Defined by the Precious Metal
2020
Hofmann-like cyanometalates constitute a large class of spin-crossover iron(II) complexes with variable switching properties. However, it is not yet clearly understood how the temperature and cooperativity of a spin transition are influenced by their structure. In this paper, we report the synthesis and crystal structures of the metal–organic coordination polymers {FeII(Mepz)[AuI(CN)2]2} ([Au]) and {FeII(Mepz)2[AgI(CN)2]2} ([Ag]), where Mepz = 2-methylpyrazine, along with characterization of their spin-state behavior by variable-temperature SQUID magnetometry and Mössbauer spectroscopy. The compounds are built of cyanoheterometallic layers, which are pillared by the bridging Mepz…
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 …
Chemical Applications of Mössbauer Spectroscopy
2012
The Tutorial Lecture begins with a brief recapitulation of the hyperfine interactions and the relevant parameters observable in a Mossbauer spectrum. The main chapter with selected examples of chemical applications of Mossbauer spectroscopy follows and is subdivided into sections on: basic information on structure and bonding; switchable molecules (thermal spin transition in mono- and oligonuclear coordination compounds, light-induced spin transition, nuclear-decay-induced spin transition, spin transition in metallomesogens); mixed-valency in biferrocenes and other iron coordination compounds, and in an europium intermetallic compound; electron transfer in Prussian blue-analog complexes; mo…