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.     

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.     

Effect of powder dispersion on the1 A 1 ⇄5 T 2 spin transition in Fe(II) complexes with 4-amino-l,2,4-triazole

A series of Fe(II) complexes with 4-amino-1,2,4-triazole ground in an agate mortar for 10 min is studied by Mössbauer spectroscopy. Strong effects of powder dispersion both on the¹ A ₁ ?⁵ T ₂ spin transition and on the structure dynamic characteristics of the complexes are found. Thus at 295 K the high-spin form of Fe(II) appears in the samples or its fraction increases; the ionicity of Fe-N bonds and the extent of distortion of the octahedral environment of iron atoms for the low-spin phases of the complexes also increase. It is established that powder dispersion markedly affects the probability of the Mössbauer effect and the vibrational spectrum of the lattice of coordination compounds. For both the low- and high-spin phases of the complexes, it is reported that the vibrational spectrum is “softened.” The main reason for these effects is supposed to be defectiveness rather than the size of the particles due to mechanical activation of the powder.     

Korrelation zwischen Mössbauer-Isomerieverschiebungen und ESCA-Bindungsenergien

Correlation between Mössbauer Isomer Shifts and ESCA Binding Energies The correlation between core-electron binding energies and Mössbauer isomer shifts is investigated and discussed for low-spin pentacyanoferrates(II), high-spin iron(III) compounds and high-spin iron(II) halides. The Fe2p_3/2 binding energies of the investigated pentacyano ferrates(II) increase with decreasing isomer shifts as a consequence of the increasing π acid strengths of the sixth ligands. In contrast, the electron binding energies in high spin iron(III) compounds and iron(II) halides increase with increasing isomer shifts. This correlation is caused by the σ donor properties and the electronegativity of the ligands.     

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.     

Thermische Zersetzung von Pentacarbonyleisen in Zeolithen des Faujasit-Typs

Thermal Decomposition of Pentacarbonyl Iron in Faujasite-Type Zeolites The nature of the iron species resulting from the title reaction has been elucidated by thermogravimetry, X-ray diffraction, electron microscopy, Mössbauer spectrometry, and by normal analytical methods. The thermal decomposition of Fe(CO)₅ adsorbed in Y-type zeolite yields pure α-Fe. In X-type zeolite Fe(CO)₅ is converted into a highly dispersed form of iron, into iron-subcarbonyl, and into high-spin Fe^II, occupying different sites of the lattice. Dealuminized zeolites adsorb Fe(CO)₅ reversibly. The estimated size of the iron(III) oxide particles formed by air oxidation is in accordance with the assumption that Fe(CO)₅ decomposes in Y-type zeolite with iron migrating to the surface of the zeolite crystals, whereas in X-type zeolite the iron remains inside the zeolite cavities.     

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.     

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.     

Anomalous spin state of iron(II) in 57Fe Mössbauer emission spectra of 57Co-Labeled tris(2-methylphenanthroline) cobalt(II) perchlorate

⁵⁷Fe Mössbauer emission spectra of the ⁵⁷Co labeled complex compound [⁵⁷Co(2-CH₃-phen)₃] (ClO₄)₂·2H₂O have been measured as a function of temperature between 293 and 4.6 K. The spectra exclusively show high-spin iron(II) resonances beside a small fraction of an high-spin iron(II) species, whereas the corresponding iron(II) compound is known to exhibit thermally induced high-spin ⁵T_2g(O_h) ? low spin ¹A_1g(O_h) transition. The electronic nature of the anomalous spin state has been found to be ⁵A₁(D₃) by a theoretical treatment of the temperature dependence of the quadrupole splitting. The results are in good agreement with those obtained from Mössbauer absorption measurements on [⁵⁷Fe_0.01Co_0.99(2-CH₃-(phen)₃] (ClO₄)₂·2H₂O.     

Transition metal-main group metal bond. VI. 199Hg NMR and 57Fe mössbauer study of (η5-C5H5)(CO)2FeHgX [X = Cl,Br,I,S2COC2H5, S2CN(C2H5)2, S2P(OC2H5)2 and Fe(CO)2(η5-C5H5)]complexes.

The ¹⁹⁹Hg NMR and ⁵⁷Fe Mössbauer spectra of iron-mercury bounded complexes are reported, compared with the ¹⁹⁹Hg NMR data for analogous molybdenum and tungsten compounds and discussed in terms of the polarization of the metal-metal bonds.     

Correlation of Mössbauer and Radiochemical Data on Hexacyanoferrate(III)

Mössbauer spectra of irradiated K₁Fe(CN)₆, observed 3 weeks after irradiation, showed that 3% of iron was converted to Fe(CN)₆^4?, while chemical analysis performed 100 hours after irradiation showed 18% was reduced to Fe(CN)₆^4?, Prussian blue was isolated in the chemical analysis, but not observed in the Mössbauer spectra. The Prussian blue formation was found to be time dependent.     

Mössbauer Studies of Bispyridine Adducts of Fe(II), 57Fe-Doped Ni(II), Co(II) and 57Co-Labelled Co(II) β-Diketonates

The Mössbauer absorption and emission spectra of FeL₂Py₂, Fe-doped (⁵⁷Fe, M) (L)₂Py₂ and ⁵⁷CoL₂Py₂ (where, L=acac, dbm and hfa, M=Co or Ni) are reported. It was found that the Mössbauer parameters, especially, quadrupole splittings of ⁵⁷Fe in ⁵⁷CoL₂Py₂ exception of ⁵⁷Co(dbm)₂PY₂are quite similar to those of the corresponding (⁵⁷Fe, Co)L₂Py₂. In addition, the Mössbauer spectra shown that the chemical states of ⁵⁷Fe in the hosts of Fe(acac)₂Py₂, Co(acac)₂Py₂ and Ni(acac)₂Py₂ were not identical.     

Naphthalene and Anthracene Complexes Sandwiched by Two {(Cp*)FeI} Fragments: Strong Electronic Coupling between the FeI Centers

The reactions of the half‐sandwich iron(II) complex [FeCl(Cp*)(tmeda)] ( 1 ; Cp*=η⁵‐C₅Me₅, TMEDA=N,N,N′,N′‐tetramethylethylenediamine) with potassium naphthalenide or potassium anthracenide gave the diamagnetic complexes [(Cp*)Fe(μ‐polyarene)Fe(Cp*)] (polyarene=naphthalene ( 2 ), anthracene ( 3a )), which have two {(Cp*)Fe} units bound to opposite faces of the polyarene. One of two {(Cp*)Fe} units in 3a is located over the central ring of anthracene while the other is positioned over an outer ring. The {(Cp*)Fe} unit bound to the central ring of 3a migrates to the outer ring upon heating in the solid state to give the isomer 3b . The electrochemical potential separations between successive one‐electron redox events for complexes 2 and 3b are large. The mixed valence complexes [ [2]+ ]⁺ and [ [3b]+ ]⁺ were synthesized by chemical oxidation. The mixed‐valence complex [ [3b]+ ]⁺ is charge delocalized on the Mössbauer timescale at 78 K, and its absorption spectrum shows an intervalence charge‐transfer band. Complex [ [2]+ ]⁺ exhibits two absorption bands in the near‐IR region and a slightly broadened doublet in the Mössbauer spectrum. DFT calculations were carried out to examine the electronic structures of these dinuclear iron(I) complexes to elucidate the factors responsible for their diamagnetism and to determine the degree of charge delocalization in the mixed‐valence complexes.     

Reactions of collman complex with tin(IV) and germanium(IV) porphyris,formation of [tin(II) and germanium(II) porphyrins] tetracarbonyliron and crystal structure of [2,3,7,8,12,13,17,18-octaethylporphinato tin(II)] tetracarbonyliron

The action of Na₂Fe(CO)₄ with tin(IV) and germanium(IV) porphyrins affords metal(II) porphyrin complexes [(por)M(II)Fe(CO)₄] (por = porphyrinate, M - Sn(II) or Ge(II)). The molecular structure of [(oep)Sn(II)Fe(CO)₄] was solved by X-ray diffraction techniques. The molecular structure of [(oep)Sn(II)Fe(CO)₄] was solved by X-ray diffraction techniques : the Sn coordination is square pyramidal with the iron in axial position (Sn-Fe = 2.492(1)Å) whereas the Fe coordination is trigonal bipyramidal. Mössbauer parameters provide convincing evidence for the formal zero oxidation state of the iron atom.     

Mossbauer Spectroscopic Study of 57Co-Labelled Cobalt(II) Bisoxine Dihydrate

The chemical states of ⁵⁷Fe atoms in ⁵⁷Co-labelled cobalt(II) oxinate and in iron(II) oxinate have been studied by means of Mössbauer spectroscopy. Consquently the trivalent charge state of iron atom was found in ⁵⁷Co-labelled hydrated cobalt(II) oxinate, and remarkable difference in Mössbauer parameters of ferrous ion in ⁵¹Co-labelled cobalt(II) oxinate and iron(II) oxinate complexes are observed.     

Preparation,Characterization, and Reactions of Dinuclear Tris(2,2,2-trichloroethoxy) Iron(III), Fe(OCH2CCl3)3

The preparation, electrical conductivity, magnetic moments, infrared, reflectance, and ⁵⁷Fe Mössbauer spectra of tris(2,2,2-trichloroethoxy) iron(III) and its adducts with some oxygen and nitrogen donor ligands are reported. Cryoscopic data of the parent compound and its complex with ethylacetate suggest these compounds to be dimeric in nitrobenzene and benzene respectively. All the compounds are covalent with Fe^III having distorted octahedral arrangement which is achieved through alkoxy bridging. The magnetic moments are lesser than those required for the spin only value indicating antiferromagnetic interactions in Fe^III atoms. The Mössbauer spectra are explained in terms of two Fe^III high spin sites corresponding to trans- and cis-positions in the structure.     

Mössbauer Studies of Bispyridine Adducts of Fe(II), 57Fe-Doped Ni(II), Co(II) and 57Co-Labelled Co(II) β-Diketonates

The Mössbauer absorption and emission spectra of FeL₂PY₂ Fe-doped (⁵⁷Fe₂M) (L)₂Py₂ and ⁵⁷CoL₂Py₂ (where, L=acac, dbm and hfa, M=Co or Ni) are reported. It was found that the Mössbauer parameters, especially, quadrupole splittings of ⁵⁷Fe in ⁵⁷CoL₂Py₂ exception of ⁵⁷Co(dbm)₂Py₂are quite similar to those of the corresponding (⁵⁷Fe, Co)L₂Py₂. In addition, the Mössbauer spectra shown that the chemical states of ⁵⁷Fe in the hosts of Fe(acac)₂PY₂, Co(acac)₂Py₂ and Ni(acac)₂Py₂ were not identical.     

Synthesis of clusters Fe2(CO)6(μ-XCH2CH=CH2)(μ3-X)Fe(CO)2Cp (X = Se, S; Cp = η5-C5H5)

The clusters Fe₂(CO)₆(μ-XCH₂CH=CH₂)(μ₃-X)Fe(CO)₂Cp (X = S, Se) were prepared by the successive treatment of the bi- and trimetallic complexes Fe₂(CO)₆(μ-Se₂) and Fe₃(CO)₉(μ₃-X) with allylmagnesium chloride and CpFe(CO)₂I. The clusters obtained contain a noncoordinated C=C bond. The structure of the Se-containing cluster was suggested on the basis of comparison of its spectral data (IR,¹H NMR, and Mössbauer spectra) with the spectra of the analogous S-containing complex, which was previously characterized by X-ray diffraction analysis.     

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.     

Spin transition in heptanuclear star-shaped iron(III)–antimony(V) NCS- and CN-bridged compounds

The precursor [Fe^III(L)Cl] (LH₂ = N,N′-bis(2′-hydroxy-benzyliden)-1,6-diamino-3-azahexane) has been prepared and Mössbauer spectroscopy assigned a high-spin (S = 5/2) state at room temperature. The precursor is combined with the bridging units [Sb^V(X)₆]^? (X = CN^?, NCS^?) to yield star-shaped heptanuclear clusters [(LFe^III–X)₆Sb^V]Cl₅. The star-shaped compounds are in general high-spin systems at room temperature. On cooling to 20 K some of the iron(III) centers switch to the low-spin state as indicated by Mössbauer spectroscopy, i.e. multiple electronic transitions. While the cyano-bridged complex performs a multiple spin transition the thiocyanate-compound shows no significant population at both temperatures.