Mössbauer spectra and electric conductivities of bidentate base bridged iron(II) phthalocyanine

Bidentate bridging base polymer complexes of iron(II) phthalocyanine FePcL, where L = pyrazine (pyz), 4,4′-bipyridine (bpy), trans-1,2-bis(4-pyridyl)ethylene (bpe), 1,2-bis(4-pyridyl)ethane (bpa) and 4,4′-trimethylene bipyridine (tmbpy), have been prepared, characterized and oxidized by iodine to give a range of iron(II) and iron(III) complexes (FePcL)_n · I_x. The electrical conductivities and Mössbauer parameters both change with respect to the kinds of bidentate bridging bases. The conjugation of bridged ligand markedly effects the conductivity of the complexes.     

Tris [2-(2′-pyridyl)benzimidazole]iron(II) complexes. Some new examples of 5T2 — 1A1 spin equilibria

Mössbauer spectra and magnetic susceptibilities for three iron (II) complexes of 2-(2′-pyridyl)benzimidazole have been measured in the temperature range 80–300°K. The results are consistent with the existence of ⁵T₂ — ¹A₁ spin equilibria in all three complexes.     

Mössbauer Studies on Spin Crossover in Schiff Bases Complexes of Iron (III)

The Mössbauer spectra of the imidazole adducts of tetradentate Schiff bases complexes of Iron (III), (FeLIm₂)⁺ have been measured. Based on the Mössbauer spectra and magnetic moments, the spin-equilibrium of Low-spin ? high-spin for [Fe(bzacen)(lm)₂)B(ph)₄ was observed.     

Crystal structure and magnetic properties of tris(2-hydroxymethyl-4-oxo-4H-pyran- 5-olato-κ2O5,O4)iron(III)

Tris(2-hydroxymethyl-4-oxo-4H-pyran-5-olato-κ²O⁵,O⁴)iron(III) [Fe(ka)₃], has been characterised by magnetic susceptibility measurements Mössbauer and EPR spectroscopy. The crystal structure of [Fe(ka)₃] has been determined by powder X-ray diffraction analysis. Magnetic susceptibility and EPR measurements indicated a paramagnetic high-spin iron centre. Mössbauer spectra revealed the presence of magnetic hyperfine interactions that are temperature-independent down to 4.2?K. The interionic Fe³⁺ distance of 7.31?Å suggests spin-spin relaxation as the origin of these interactions.     

Mononuclear iron(III)macrocyclic complexes derived from 4-methyl-2,6-di(formyl/benzoyl)phenol and diamines: synthesis,spectral speciation and electrochemical behaviour

Two series of macrocyclic iron(III) complexes of stoichiometry [Fe(L)Cl₂]Cl (1, 2) have been synthesised and characterised. Compounds belonging to series 1 are derived from 4-methyl-2,6-diformylphenol and diamines (H₂L), and those of 2 from 4-methyl-2,6-dibenzoylphenol and diamines. All the brown complexes have been characterised by physicochemical techniques. The mass, infrared, electronic, ESR and Mössbauer spectroscopies, magnetic susceptibility data, molar conductance, X-ray diffraction and cyclic voltammetric studies provide unambiguous evidence that 1 and 2 are high-spin iron(III) complexes in which the metal has an octahedral geometry. The Mössbauer data are consistent with high-spin iron(III) and substantial covalency in the Fe(III)–ligand bonds. Cyclic voltammetric studies in DMSO of the mononuclear iron(III) complexes show that they undergo quasi-reversible reduction with E_1/2 approximately −0.74 V versus SCE.     

Mössbauer Spectra and Magnetic Properties of Polydiimine Complexes of Iron(II) Sulfate

A new series of polynuclear iron complexes with polydiimine ligand have been prepared from the Schiff-base condensation of pyridine-2, 6-dialdehyde or 2, 6-diacetylpyridine with aliphatic diamines. The structures of the complexes are represented by [?N = CR-Py-CR = N-(CH₂)_n-]₂FeSO₄·xH₂O; where R = H, CH₃; n = 4?10, × = 5～8. Mössbauer spectra and magnetic measurements show several complexes have unusual magnetic properties.     

57Fe Mössbauer and 31P NMR Spectroscopic Characterisation of Fe(CO)3L2 Complexes (L=Phosphite and Phosphine)

Abstract

A series of mixed ligand complexes of the type [Fe(CO)₃L¹L²] (L¹=tri-phenylphosphite and L²=phosphine or phosphite) have been prepared to study the Fe-P bond. The ⁵⁷Fe Mössbauer spectra of trans-[Fe(CO)₃L¹L²] showed a quadrupole splitting doublet characteristic of the disubstituted iron carbonyls in trigonal bipyramidal symmetry. The linear dependence of the quadrupole splittings on the isomer shifts with a positive slope has revealed that the iron-to-phosphorus σ-donation is offset by the phosphorus-to-iron π-back donation. The ³¹P{¹H} NMR spectra showed a couple of doublets assigned to the coordinated phosphite and the coordinated phosphine. The doublet of the phosphite site was generally observed at the down field compared with that of the phosphine site. The coordination shifts increase with the Mössbauer isomer shifts, suggesting that the iron-to-phosphorus π-back donation plays an important role in the Fe-P bond of trans-[Fe(CO)₃L¹L²]. The relatively large coupling constants due to ²J(P,P) have demonstrated that there exists a strong interaction between trans phosphorus ligands through the d_π orbitals of the central iron. The coupling constant is a measure of the bond strength between Fe-P, while the Mössbauer isomer shift reflects the electron density at the iron nucleus. Thus, a linear correlation has been established between these two spectroscopic parameters.     

Mössbauer spectroscopic evidence for iron(III) complexation and reduction in acidic aqueous solutions of indole-3-butyric acid

Mössbauer spectroscopic studies were carried out in acidic (pH 2.3) ⁵⁷Fe^III nitrate containing aqueous solutions of indole-3-butyric acid (IBA), rapidly frozen in liquid nitrogen at various periods of time after mixing the reagents. The data obtained show that in solution in the presence of IBA, iron(III) forms a complex with a dimeric structure characterised by a quadrupole doublet, whereas without IBA under similar conditions iron(III) exhibits a broad spectral feature due to a slow paramagnetic spin relaxation which, at liquid nitrogen temperature, results in a large anomalous line broadening (or, at T = 4.2 K, in a hyperfine magnetic splitting). The spectra of ⁵⁷Fe^III+IBA solutions, kept at ambient temperature under aerobic conditions for increasing periods of time before freezing, contained a gradually increasing contribution of a component with a higher quadrupole splitting. The Mössbauer parameters for that component are typical for iron(II) aquo complexes, thus showing that under these conditions gradual reduction of iron(III) occurs, so that the majority (85%) of dissolved iron(III) is reduced within 2 days. The Mössbauer parameters for the iron(III)-IBA complex in aqueous solution and in the solid state (separated from the solution by filtration) were found to be similar, which may indicate that the dissolved and solid complexes have the same composition and/or iron(III) coordination environment. For the solid complex, the data of elemental analysis suggest the following composition of the dimer: [L₂Fe-(OH)₂-FeL₂] (where L is indole-3-butyrate). This structure is also in agreement with the data of infrared spectroscopic study of the complex reported earlier, with the side-chain carboxylic group in indole-3-butyrate as a bidentate ligand. The Mössbauer parameters for the solid ⁵⁷Fe^III-IBA complex at T = 80 K and its acetone solution rapidly frozen in liquid nitrogen were virtually identical, which indicates that the complex retains its structure upon dissolution in acetone.     

Spectroscopic and structural properties of homonuclear Fe(II) pyrazine-bridged polymeric complexes [Fe(pyrazine)2X2]n. (X = Cl,Br or I)

The reactions of FeX₂ (X = Cl, Br or I) with pyrazine (pyz) yield the Fe(pyz)₂X₂ compounds. Examination of IR and Raman spectra in the medium- and far-IR region as well as studies of electronic and Mössbauer spectra suggests that the complexes contain six-coordinate high-spin Fe(II) in the FeN₄X₂ chromophore. The complexes have a polymeric pseudo-octahedral pyz-bridged structure. The magnetic moments are independent of temperature and low-temperature magnetic measurements do not indicate any magnetic ordering above 4.2 K in these compounds. The π-acceptor properties of pyz are reflected both in the electronic spectra evaluated in terms of the angular overlap model and the Mössbauer parameters.     

First order magnetic transition,magnetic structure,and vacancy distribution in Fe2P

The para- to ferromagnetic transition in Fe₂P has been studied using Mössbauer spectroscopy. The magnetic hyperfine fields drop abruptly from about half of their saturation values to zero at 214.5 K indicating a first order transition. The isomer shifts show a discontinuous change at the transition point. For some samples the transition takes place over a wide temperature range, probably due to impurities and other imperfections in the samples. From the magnetic hyperfine fields at 15 K the magnetic moments can be deduced to be 1.14 μ_B and 1.78 μ_B for Fe(1) and Fe(2), respectively. An assignment of the components in the Mössbauer spectra to the two crystallographically nonequivalent iron positions has been made from the temperature variation of the spectra.The ordering of metal vacancies has been investigated by a Mössbauer study of a nonstoichiometric Fe₂P sample and by an X-ray diffraction study of a nonstoichiometric Mn₂P crystal.     

Mössbauer Spectra of the Complexes of Iron(II) Bichloride with Monoacetyl and 1, 1′-Diacetylferrocence Thiosemicarbazone

Complexes of iron(II) dichloride with monoacetyl and 1, 1′-diacetylferrocence thiosemicarbazone have been prepared and characterized by means of optical spectra and magnetic measurement, and these structures have been investigated by Mössbauer spectra. It is inferred that the structures for iron(II) complexets of monoacetylferrocence thiosemicarbazone and 1, 1′-diacetylbis (thiosemicarbazone) are monomer and polymer respectively.     

SINGLET-TRIPLET SPIN TRANSITION IN AN IRON(II) COMPLEX OF 1,10-PHENANTHROLINE-2-CARBOTHIOAMIDE

Abstract

The ⁵⁷Fe Mössbauer effect for the solid complex FeLCl₂·H₂O (L=10-phenanthroline-2-carbothioamide) has been studied between 4.2°K and 298°K. Two overlapping doublets (I and II) are observed, their relative intensity being strongly temperature dependent. The doublets are characterized by δE_Q(I)=0.53 mm sec^?1, δ^IS(I)=+ 0.22 mm sec^?1 and δE_Q(II)=1.33 mm sec^?1, δ^IS(II)=+0.23 mm sec^?1 at 4.2°K. In conjunction with magnetic data, the Mössbauer spectra are interpreted in terms of a singlet-triplet spin transition of the central iron(II) ion. In an applied magnetic field at 4.2°K, H_int=0, V_ZZ(I)>0, and V_ZZ(II)>0. The results are consistent with optical electronic and infrared vibrational spectra.     

Crystal structure and the magnetic properties of tris(2-chloromethyl-4-oxo-4H-pyran-5-olato-κ2O5,O4)iron(III)

The tris(2-chloromethyl-4-oxo-4H-pyran-5-olato-κ²O⁵,O⁴)iron(III), [Fe(kaCl)₃], has been synthesized and characterized by the crystal structure analysis, magnetic susceptibility measurements, Mössbauer, and EPR spectroscopic methods. The X-ray single crystal analysis of [Fe(kaCl)₃] revealed a mer isomer. The magnetic susceptibility measurements indicated the paramagnetic character in the temperature range of 2 K–298 K. The EPR and Mössbauer spectroscopy confirmed the presence of an iron center in a high-spin state. Additionally, the temperature-independent Mössbauer magnetic hyperfine interactions were observed down to 77 K. These interactions may result from spin–spin relaxation due to the interionic Fe³⁺ distances of 7.386 Å.     

Temperature dependence of the Mössbauer spectrum and magnetic susceptibility [Fe(uridine)Cl2]∞: Novel magnetic ordering of transition metal complexes based on nucleoside ligands

The zero-field Mössbauer spectra and magnetic susceptibility of a polycrystalline sample of the polymeric material [Fe(uridine)Cl₂]_∞ have been measured in the temperature range 1.7-300 K. The compound exhibits two magnetic transitions. The isomer shift and quadrupole splitting indicate a distorted pseudo-octahedral FeCl₄O₂ chromophore resulting from condensation to a network structure via chloro and uridine ligand bridging.     

Synthesis and spectroscopic characterization of new metal(II) complexes with methionine sulfoxide

Methionine sulfoxide complexes of iron(II) and copper(II) were synthesized and characterized by chemical and spectroscopic techniques. Elemental and atomic absorption analyses fit the compositions K₂[Fe(metSO)₂]SO₄·H₂O and [Cu(metSO)₂]·H₂O. Electronic absorption spectra of the complexes are typical of octahedral geometries. Infrared spectroscopy suggests coordination of the ligand to the metal through the carboxylate and sulfoxide groups. An EPR spectrum of the Cu(II) complex indicates tetragonal distortion of its octahedral symmetry. ⁵⁷Fe Mössbauer parameters are also consistent with octahedral stereochemistry for the iron(II) complex. The complexes are very soluble in water.     

Mössbauer Spectroscopic Studies of Supported α-Fe2O3 and Fe Catalysts II: The Effect of the Second Metal Addition

The effect of the addition of a second metals such as Zn and Ni on the calcinaton and reduction of alumina, magnesia and silicasupported iron catalysis with total iron loading of 5wt% is investigated by Mössbauer spectroscopy. It is shown that the reducibility of supported α-Fe₂O₃ is gradually increased by adding the second metal. The values of the magnetic hyperfine field obtained from Mössbauer spectra for the Zn or Ni-added α-Fe₂O₃ or Fe catalysts decreased with increasing second metal loading.     

Iron(III)5(2′-hydroxyphenyl)-3-(4-X-phenyl)pyrazolinates and their addition complexes with N,P donor ligands: synthesis,spectral and antimicrobial investigations

Iron(III)5(2′-hydroxyphenyl)-3-(4-X-phenyl)pyrazolinates of the type (C₁₅H₁₂N₂OX)₃Fe [where X =–H,–Cl,–CH₃,–OCH₃] have been synthesized by reaction of anhydrous FeCl₃ with the sodium salts of pyrazoline in 1 : 3 molar ratio. Their addition complexes with N and P donor ligands [2,2′-bipyridine, 1,10-phenanthroline and triphenylphosphine] were prepared in 1:1 molar ratio. These newly synthesized derivatives have been characterized using elemental analysis (C, H, N and Fe), molecular weight measurement, magnetic moment data, FAB mass, ³¹P NMR and Mössbauer spectral data. The complexes have been examined for crystalline/amorphous nature through XRD; all complexes are amorphous. Octahedral geometry around iron(III) confirms the presence of three bidentate pyrazoline ligands in iron(III)5(2′-hydroxyphenyl)-3-(4-X-phenyl)pyrazolinates. In addition complexes pyrazoline is monodentate. The bidentate and monodentate behavior of pyrazoline ligands was confirmed by IR spectral data. All the complexes were tested for their in-vitro antimicrobial activity. The metal complexes and their adducts exhibit better antibacterial and antifungal activity than the pyrazolines.     

Mössbauer study of the corrosion products of iron

Investigations of the possible use of Mössbauer measurements for the analysis of the corrosion products of iron are reported. The Mössbauer spectrum was measured at room and liquid nitrogen temperatures on two samples produced by different corrosion procedures. The isomeric shift, quadrupole splitting and magnetic splitting observed in the spectra yield information on the chemical composition. In this way, the chemical forms of the compounds in the samples could be established. The magnetic properties, revealed by the spectra taken at different temperatures, permitted the identification of the polymorphous modifications. The rust produced in air saturated with water vapour was found to consist of 50% (w/w) Fe₂O₃,～40% γ-FeOOH, and ～10% β-FeOOH, while the rust produced by periodical immersion in saturated calcium chloride solution is composed of about equal amounts of β-FeOOH and γ-FeOOH. These findings have been confirmed by the thermoanalytical curves of the samples. The Mössbauer effect presents a convenient method for the investigation of the corrosion products of iron.     

A Mössbauer spectroscopy investigation of the Intergrowth Phases LaSr3Fe3−xMx010−δ (M = Al,Cu)

Iron-57 Mössbauer spectroscopy confirms a high sensitivity of the three-dimensional magnetic ordering temperature (T_Néel) for a series of new intergrowth phases to both oxygen stoichiometry and the partial substitution of iron by copper and aluminium in the Ruddlesden-Popper phase LaSr₃Fe₃0_10?δ. The chemical isomer shifts suggest that significant covalent electron delocalization exists in these phases. Spectra for the paramagnetic phases indicate two distinct iron coordination environments consistent with x-ray and neutron diffraction structure determinations. The Mössbauer spectra at 4.8 K exhibit the overlap of two magnetic hyperfine patterns corresponding to cooperative magnetic order at the iron sites with internal fields of 45 and 27 Tesla for nominal Fe³⁺ and Fe⁴⁺ sites respectively.     

BINUCLEAR COMPLEXES OF IRON(III) WITH SALICYLATE LIGANDS

Abstract

Binuclear iron(III) complexes with salicylate ligands, Na₂ [Fe₂ (C₇ H₄ O₃)₄ (H₂O)₂] and Na₄ [Fe₂ (C₇H₄O₃)₄ (OH)₂], crystallize out in the pH range 1–5 and pH 5.5, respectively, from solutions containing iron(III) chloride and a slightly more than two molar proportion of sodium salicylate. Infrared and Mössbauer spectral results and magnetic moment data indicate the presence of non-linear Fe—O—Fe bridge bonds. Evidently two salicylate ligands form bridges between the two iron(III) ions through phenolic oxygen. Mössbauer spectral results indicate the absence of bridging salicylate ligands in solutions of the complex prepared by mixing iron(III) chloride and two to three-fold molar excess of salicylate ions; only mononuclear complexes exist in such solutions.