An unusual example of a rapid spin-equilibrium iron complex

Bis(N-(1-benzoyl-2-propylidene)-2-pyridylmethylaminato)iron(III) hexafluorophosphate (Fe(bzpa)₂PF₆ is shown to be a spin-equilibrium compound between low- (S = $\text{1}\text{2}$) and high- (S = $\text{5}\text{2}$) spin states depending on temperature, and to have the unusual property that the relaxation time of the spin change is shorter than the Mössbauer lifetime (1 × 10^?7s) of iron- 57 (l = $\text{3}\text{2}$) in the solid state.     

The spin 32 state (?) in six-coordinate iron (III). A Mössbauer and EPR investigation

Tris-(4-morpholinecarbodithioato-S,S′) iron (III) (FeM) and its dichloromethane solvate, (FeM·CH₂Cl₂), have been prepared and their temperature-dependent Mössbauer and EPR spectra have been determined at temperatures between liquid nitrogen and ambient. The Mössbauer spectra of FeM·CH₂Cl₂ differ considerably from that of FeM and is interpreted in terms of a four-line spectrum at 77 K. The EPR spectra of the two complexes indicate that the lower spin state of FeM·CH₂Cl₂ populates much more rapidly in the temperature range studied (100–300 K) than does FeM. These results support the postulation of an S = $\text{5}\text{2}$ ? S = $\text{1}\text{2}$ spin-equilibrium for FeM and a corresponding S = $\text{5}\text{2}$ ? S = $\text{3}\text{2}$ equilibrium for FeM·CH₂Cl₂.     

Mössbauer effect study and magnetic properties of a ferromagnetic homologue of bromobis(diethyldithiocarbamato)iron(III)

Mossbauer spectroscopy and magnetic susceptibility properties of a crystal modification of the title complex, denoted Fe(dtc)₂Br, show that the iron atoms in this material become ferromagnetically ordered with T_c = 1.52 × 0.02 K. This result is consistent with a magnetic specific heat anomaly recently observed in similar material by Yoshikawa et al. Mössbauer effect hfs show that the lower Kramers doublet from the orbital singlet, spin quartet ground term is of composition |S = $\text{3}\text{2}$, M_S = ± $\text{1}\text{2}$).     

Nature of satellites in x-ray photoelectron spectra XPS of paramagnetic cobalt (II) compounds

XPS spectra of a number of paramagnetic Co(II) compounds are studied and the correlation between the intensity of the Co 2_{p$\text{3}\text{2}$} satellite and the magnitude of its magnetic moment is shown. A new approach is put forward to explain the experimental data.     

Mössbauer spectra,magnetic and electrical behavior of Ba1+xFe2S4 phases

The Mössbauer spectra, and magnetic and electrical properties of Ba_1+xFe₂S₄ infinitely adaptive phases with 0.074 ≤ x ≤ 0.142 and of BaFe₂S₄ were studied. The properties are highly anisotropic because of the presence in the structure of one-dimensional infinite chains of edge sharing FeS₄ tetrahedra. BaFe₂S₄ is a semiconductor, E_g = 0.66 eV; magnetic susceptibility can be fit by a one-dimensional Heisenberg model with spin $\text{5}\text{2}$ and $\text{J}\text{k}\text{= ?30°}\text{K}$. The Ba_1+xFe₂S₄ phases have Curie-Weiss behavior with an effective moment of about 2 B.M. The moment increases with x. These phases are metallic. The Mössbauer isomer shift varies linearly with valence, increasing with increasing x. The single quadrupole split absorption line characteristic of these compounds disappears at about 270°K and a complex spectrum consisting of overlapping hyperfine patterns appears at lower temperatures. Magnetic short-range ordering is responsible for this behavior although the susceptibility in this temperature range does not reflect this effect.     

Mixed ugand complexes of iron(III) derived from its dithiocarbamato complexes

Three different types of iron(III) complexes, Fe(A)₃, Fe(A)₂(A') and Fe(A)(A')₂, whereA is either piperidyldithiocarbamate or morpholyl dithiocarbamate andA' is glycine(oxine) acetylacetone have been prepared by reacting Fe(III) salt with sodium salt of piperidinedithiocarbamic acid or morpholine-dithiocarbamic acid and acetylacetone(oxine)-glycine in different ratios. The mixed ligand complexes have been characterised by elemental analysis, magnetic susceptibility measurements, infrared, electronic spectral techniques and by thermal analysis. Electronic spectral studies suggests that all the complexes possess distorted octahedral geometry. The magnetic moment of the high spin iron(III) complexes lies in the range of 5.88–6.00 and for low spin lies in the range of 3.36–4.34 B.M. TG studies show one step decomposition of complexes and formation of Fe₂O₃ at the end of the step.     

The structure of iron(III) complexes with carbamide derivatives

Infrared spectra of new iron(III) complexes with urea derivatives: [Fe (CH₃HNCONH₂)₆]X₃; [Fe(C₂H₅HNCONH₂)₆]X₃ and [Fe(CH₃-HNCONHCH₃)₆]X₃ (where X = Cl^?, NO^?₃ or $\text{1}\text{2}$SO^2?₄) have been recorded and their interpretation given. The analysis of the infrared spectra was based on a comparison of the positions of bands corresponding to the vibrations of characteristic groups appearing in the complexes and the free ligands. Comparison and analysis of the data show that the urea derivatives coordinate with mono- and disubstituted iron(III) through the oxygen atom of the carbonyl group.     

Paramagnetische organothalliumverbindungen in lösung: I. Esr-untersuchungen von diphenyl-thallium(III)-tonenpaaren mit brenzcatefechinen,pyrogallolen und 1,2-diketonen

Diphenylthallium hydroxide reacts very smoothly in organic solvents with catechols, pyrogallols and 1,2-diketones to stable paramagnetic diphenylthalliumsemiquinone and diphenylthalliumsemidione complexes respectively. This reaction has been investigated with 43 different ligands in numerous solvents. Therefore its general application is proofed.The ESR-spectra of these solutions show the hydrogen hyperfine structure of the ligands and an unusual large coupling which we assign to magnetic interaction of the free electron with the ²⁰³Tl and ²⁰⁵Tl nuclei. The thallium splittings observed depend remarkably on the ligands used. We refer this to different solvation phenomena.Semiquinones of the pyrogallol type show on principle two different radical types. Small concentrations of diphenylthallium hydroxide produce $\text{1}\text{1}$ complexes. These can be converted into $\text{1}\text{2}$ complexes by addition of further amounts of diphenyl thallium hydroxide.The ESR-spectra of the semiquinone-and the semidione-thallium complexes exhibit an unusually strong solvent dependence of the thallium coupling and of the g-factor. It is possible to explain both variations uniformly by the different donor ability of the solvents used.All complexes investigated indicate remarkable temperature dependence of the thallium splitting and the g-factor. The thallium couplings show a positive temperature gradient whereas the g-factor decrease with increasing temperature as expected.Based on the sum of the observed effects, we assume that the radicals observed by us are ion pairs in which a diphenylthallium cation interacts with the semiquinone- or semidione-anion, respectively.     

Magnetic Properties and Mössbauer Spectra of Binuclear Copper(II) and Tetranuclear Diiron(III)-porphyrin-dicopper(II) Complexes with Schiff-Base Ligands of 2-lmidazolealdehyde and Acetylpyrazine

The binuclear copper(II) and tetranuclear diiron(III)-porphyrin-dicopper(II) complexes with the Schiff-base ligands of N,N′-bis(2-imidazolaldehyde)ethylenediimine, N,N′-bis(2-imidazolaldehyde)-p-phenyldiimine, N,N-bis(acetylpyrazine)-ethylenediimine and N,N′-bis(acetylpyrazine)-p-phenyldiimine have been prepared and characterized. The magnetic data indicated that the spin ground states and the magneic interaction between Cu(II)-Cu(II) or Fe(III)-Cu(II) are dependent on the nature of the bridging ligands. A weak antiferromagnetic interaction between Fe(III) and Cu(II) is evident from the temperature-dependent magnetic measurements. The Mössbauer spectra of iron(III) -porphyrin sites showed an asymmetric quadrupole doublet consistent with high-spin iron(III) S = 5/2.     

Hyperfine splitting in the ESR spectra of random oriented alkali earth biradical chelates

The ESR spectra of rigid glass solutions of biradicals of glyoxal diimine anions and alkali earth cations were recorded. The spectra could be computer simulated only by adding to the spin hamiltonian

= gβH·S + D[S_Z²?$\text{1}\text{2}$S(S+1)] a hyperfine term due to the anisotropic interaction of the nitrogen nuclei. Two different models were tested: the first one with the two radicals in the same plane and the second one with the two radicals perpendicular; agreement with the experiment was found for the latter.     

Preparation,structure, and magnetic properties of isostructural La3MAlS7 and La3MFeS7 (M = Mg,Mn, Fe,Co, Ni,or Zn)

A series of quaternary metal sulfides of the general formula La₃MM′S₇ (M = Mn, Fe, Co; M′ = Al and M = Mg, Mn, Fe, Co, Ni; M′ = Fe) consisting of linear chains of face shared MS₆ octahedra and isolated M′S₄ tetrahedra has been prepared and studied. The aluminium compounds La₃MAlS₇ (M = Mn, Fe, Co) exhibit linear chain antiferromagnetism. Magnetic behavior of other La₃MFeS₇ sulfides has been examined in detail. The magnetic susceptibility of La₃MgFeS₇ shows that tetrahedral site Fe³⁺ undergoes a transition from $\text{S =}\text{5}\text{2}$ to S = 2 spin state around 150 K.     

Effect of the nature of axial ligand on the effective charge of the metal center in PcFe(II) complexes

Disubstituted iron phthalocyanine complexes were studied by X-ray photoelectron spectroscopy (XPS). Fe2p _3/2, N1s, and C1s XPS spectra were analyzed, and the role of the ligand in their generation was determined. Assignment of the magnetic properties of phthalocyanine iron complexes was done. Covalence of the metal-ligand bond was determined. The nature of the axial ligand in Pc^tFe affects the electronic state of the central iron atom.     

Synthesis and characterization of an iron(III) complex of glycine derivative of bis(phenol)amine ligand in relevance to catechol dioxygenase active site

A glycine derivative of bis(phenol)amine ligand (HL^Gly) was synthesized and characterized by ¹H NMR and IR spectroscopies. The iron(III) complex (L^GlyFe) of this ligand was synthesized and characterized by IR, UV-Vis, X-ray and magnetic susceptibility studies. X-ray analysis reveals that in L^GlyFe the iron(III) center has a distorted trigonal bipyramidal coordination sphere and is surrounded by an amine nitrogen, a carboxylate and two phenolate oxygen atoms. The mentioned carboxylate group acts as μ-bridging ligand for iron centers of neighbor complexes. The variable-temperature magnetic susceptibility indicates that L^GlyFe is the paramagnetic high spin iron(III) complex. It has been shown that electrochemical oxidation of this complex is ligand-centered due to the oxidation of phenolate to the phenoxyl radicals. The L^GlyFe complex also undergoes an electrochemical metal-centered reduction of ferric to ferrous ion. The oxygenation of 3,5-di-tert-butyl-catechol, with L^GlyFe in the presence of dioxygen was investigated.     

Electrochemistry of the iron-sulfur cluster compound [(η-C5H5)2Fe2S2(SC2H5)2]. Synthesis and propeties of the oxidation products

In order to gain some insight into the stability of configuration and the bonding in the novel disulfide-containing complex [(η-C₅H₅)₂Fe₂S₂(SC₂H₅)₂], electrochemical properties of this compound and its SCH₃ and SCH₂C₆H₅ analogues were studied in various solvents and the magnetic properties of a subsequently isolated paramagnetic monocation were investigated. The cyclic voltammogram of [(η-C₅H₅)₂Fe₂S₂(SC₂H₅)₂] shows a reversible one-electron oxidation at E_{$\text{1}\text{2}$}= +0.21 V and a quasi-reversible one-electron oxidation at E_{$\text{1}\text{2}$} = +0.90 V (vs.saturated calomel electrode). The stable monocation has been electrochemically synthesized and the magnetic suceptibility shows a simple paramagnetic behavior with one unpaired electron per dimeric unit. Frozen solutions of this species at 103K yielded anisotropic ESR spectra with g₁ = 2.135, g₂ = 1.976, and g₃ = 1.934. Labeling the complex with ³³S in the disulfide bridge resulted in no observable hyperfine splitting or line broadening in the ESR. The dicationic species is unstable with respect to loss of the S₂ bridge and formation of a solvent-ligated dication, [(η-C₅H₅)Fe(NCCH₃)(SC₂H₅)]₂²⁺, isolated by electrolysis of the monocation at +1.2 V in CH₃CN.     

Iron(III) amino acid complexes: evidence for the existence of a spin equilibrium

lron(III) amino acid complexes of general composition Fe(amino acid)(OH)Cl·2CH₃OH were synthesized and investigated. The analytical and other physical data support this formulae. The spectral, variable-temperature magnetic and Mössbauer data suggest the presence of a spin equilibrium involving S = 1/2 and S = 3/2 spin states, and this is attributed to the large distortions in the compounds.     

Iron(II) and Iron(III) Perchlorate Complexes of Ciprofloxacin and Norfloxacin

The reactions of ciprofloxacin (CIP) and norfloxacin (NOR) with iron(II) and iron(III) perchlorate have been investigated. The optical spectra support the formation of four complexes for each oxidation state with 1 : 1, 1 : 2, 1 : 3 and 1 : 4 metal to ligand molar ratios. The electrical conductivity and magnetic susceptibility measurements show that the isolated complexes are high spin and the Fe(ClO 4 ) 2 and Fe(ClO 4 ) 3 complexes behave as 1 : 2 and 1 : 3 electrolytes, respectively. The IR spectra indicate that CIP and NOR bind to the iron ion as bidentate ligands through the carbonyl oxygen atom and one of the oxygen atoms of the carboxylate group.     

Epr of luminescent glasses containing chromium(III)

The EPR spectrum at 9 19 GHz has been examined for a series of chromium(III)-doped glasses. The S = $\text{3}\text{2}$ chromium ion site in all the glasses displays two prominent transitions in the g = 6 and g = 2 region. Concentration-dependent broadening observable in the glasses at g = 2 is associated with isotropic spin exchange and provides evidence that the concentration-dependent quenching of chromium luminescence in glasses is due to an ion pairing mechanism     

Polarographic determination of iron(II) and iron(III) complexes with edta

The iron(II) and iron(III) complexes with EDTA can be determined separately and in mixtures in acetate-buffered medium at pH 4.0. The E_{$\text{1}\text{2}$}values are in the range ?0.105 to ?0.112 V vs. SCE. Linear calibration plots are obtained over the range 0–1.0 mM for each oxidation state. A sample-handling procedure for avoiding oxidation of iron(II) species is described. It is shown that the acetate buffer system does not affect the stability of the iron-EDTA complexes.