Towards an understanding of the quadrupole splittings found in the Mössbauer spectroscopic data of a number of substituted tetraphenylporphyriniron(III) halides

Mononuclear and μ-oxo-dimers of a series of unsymmetrical substituted tetraphenylporphyriniron(III) complexes have been prepared and studied using Mössbauer spectroscopy. The Mössbauer data are discussed and compared to the other known data for similar high spin Fe(III) porphyrinsA good correlation between Hammet σ_R° (the mesomeric values) of the porphyrin substituent and the Mössbauer quadrupole splitting (Δ) has been found.     

Reactions of matrix isolated fron atoms with nitric oxide

The matrix isolated binary nitrosyls, Fe(NO)_x, x ⩽ 4, formed upon co-condensation of iron with nitric oxide have been studied by infrared and Mössbauer spectroscopies. Infrared data suggest that the unsaturated complexes (x = 1, 2) contain linear NO ligands. The isomer shifts of all four complexes are consistent with covalently bonded Fe(0). In 100% NO, Fe(NO)₄ is the major product and gives the identical Mössbauer spectrum as Fe(NO)₄ made from the high pressure reaction of Fe(CO)₅ with NO. In addition, a second product, probably Fe(NO)₃ is detected in the Mössbauer spectmm of Fe(NO)₄ made by both procedures. Evidence is seen for a partially reversible temperature dependent equilibrium between Fe(NO)₃ and Fe(NO)₄, with Fe(NO)₄ favored at low temperatures. The unusal reactivity of NO with iron atoms is discussed.     

A Mössbauer spectroscopic study of [phthalocyaninato tin(IV) tetracarbonyl iron(0)]

The action of Na₂Fe(CO)₄ and bis(chloro)phthalocyaninato tin(IV) yields phthalocyaninato tin(IV) tetracarbonyl iron(0). Mössbauer spectroscopic studies on the product indicate no change in formal oxidation state need be invoked to account for the formation of the metal-metal bond.     

Synthesis of diorganotin(IV) complexes with nucleosides and their Characterization by Mössbauer and infrared spectroscopy

A number of new complexes of R₂Sn^IV with adenosine, guanosine, inosine, cytidine and uridine were synthesized by reaction of ribonucleosides with diorganotin oxide in hot methanol. The complexes were characterized by infrared and ¹¹⁹Sn Mössbauer spectroscopy as O(2′), O(3′) (diorganostannylene) nucleosides; the occurence of dimers with three-co-ordinate oxygen atoms is inferred on the basis of spectroscopic data.     

(n-Bu4N)[Fe(cbdt)2]: Synthesis,crystal structure and magnetic characterisation of a new FeIII bisdithiolene complex

The synthesis of the dithiol precursor of the new ligand 4-cyanobenzene-1,2-dithiolate (cbdt) is described. The (n-Bu₄N)[Fe(cbdt)₂] complex, was prepared and characterised by X-ray diffraction, Mössbauer spectroscopy and magnetisation measurements. The crystal structure consists in cis [Fe(cbdt)₂]- units dimerised in a trans fashion, with Fe in a square pyramidal coordination, the dimers being well isolated from each other by the cations. The magnetic susceptibility shows that the [Fe(cbdt)₂]^? units have a S = 3/2 spin configuration.     

Synthesis and 121Sb mössbauer study of a number of organoantimony(III) compounds containing antimony-main group V element bonds

The synthesis of organoantimony(III) compounds of the type R₂SbMR′₂ in which R,R′=Et or Ph and M=N, P or As has been investigated. Diphenylaminodiethylstibine and diphenylaminodiphenylstibine were successfully synthesized. Attempts to prepare phosphinostibines and arsinostibines of the type R₂SbMR′₂ (M=P, As) failed and resulted in the formation of the corresponding diphosphines, diarsines, and distibines Only in the case of the synthesis of Ph₂AsSbPh₂ was an analytically pure product obtained. A series of antimony(III) compounds containing antimony-main group V element bonds has been investigated by ¹²¹Sb Mössbauer spectroscopy. The near consistency in the isomer shift (−4.0 to −4.6 mm/s relative to InSb) implies almost no change in the s-character in the total antimony-ligand bonds. Variation in the values of the quadrupole coupling constant and the asymmetry factor are discussed in terms of structure and/or changes in the p-character of the antimony-ligand bonds.     

Some μ-oxo compounds of iron-hemiporphyrazine. Synthesis and properties

Details of the conditions necessary for preparing the recently reported μ-oxo-ironhemiporphyrazinate compounds (Fe(IV)hpO)_n and [(Fe(III)hp)₂O]H₂O are given. Two further homologous μ-oxo Fe(III)hemiporphyrazinates are described: an amorphous μ-oxo dimer and a μ-oxo dimer HCl adduct. The thermal and spectroscopic (UV-Vis, IR, Mössbauer, XPS) properties and magnetic susceptibilities of these compounds have been investigated. The reducibility of these species in solution, in the presence and absence of O₂, has been monitored. The results do not indicate a change in oxidation state of the iron in (FehpO)_n. Attempts to obtain the hemiporphyrazinato Fe(III) chloride are described.     

Complexes of diphosphaferrocenes with Lewis acids and Cu(I), Ag(I) salts

Complexes of diphosphaferrocenes have been prepared using (a) Lewis acids BF₃·Et₂O, A1C1₃ and (b) Cu(I) and Ag(I) salts. The ³¹P spectra showed that BF₃·Et₂O complexes at phosphorus (characterised by a large downfield shift of 103 ppm) whereas all the other adducts involved binding at iron (characterised by large upfield shifts of 36–94 ppm). Deep purple adducts were isolated and characterised for the reaction of 2, 2′, 5, 5′-tetraphenyldipho sphaferrocene with silver trifluoroacetate and triflate and also with copper(I) iodide. Similar complexes were isolated from 3, 3′, 4, 4′-tetramethyldiphosphaferrocene. ⁵⁷Fe Mössbauer spectroscopy of the adducts showed that unlike the ferrocene system, quadrupole splittings generally decreased on iron complexation. The results are discussed in terms of current MO theory of ferrocene and diphosphaferrocene.     

Preparation and properties of Fe3+-amino acid complexes: Crystalline complexes with aliphatic amino acids

Crystalline complexes of Fe³⁺ and several aliphatic amino acids have been prepared. All have a basic molecular constitution [Fe[AA]₂H₂O]₃O (ClO₄)₇, as determined by optical, magnetic, and Mössbauer measurements. The physical properties of these compounds display a marked similarity to those of ferritin.     

125Te Mössbauer spectra of the intercalation compound (Te2)2(I2)

The quadrupole split asymmetric ¹²⁵Te Mössbauer spectrum recorded from the compound (Te₂)₂(I₂), in which monomolecular planar layers of iodine molecules are intercalated between layers of tellurium, is a reflection of the distorted environment of tellurium atoms in a two-dimensional layered compound in which the elongated flat crystals are preferentially orientated. The differences between the Mössbauer parameters recorded from (Te₂)₂(I₂) and those recorded from elemental tellurium and the tellurium(0) species in the compound Te₃Cl₂ are associated with small differences between the environments of tellurium in the three compounds. The Mössbauer spectra recorded from (Te₂)₂(I₂) are consistent with a recently proposed model on which the electronic band structure of (Te₂)₂(I₂) has been derived.     

New stannylene-bridged tetracarbonyliron dimers

The reaction of three stannocene derivatives, bis(pentamethylcyclopentadienyl)tin(II) cyclopentadienyltin(II) chloride and cyclopentadienyltin(II) bromide with diiron nonacarbonyl yielded three new stannocene tetracarbonyliron compounds. Infrared, NMR and Mössbauer spectra of the products indicate that they are new members of a class of dimeric stannylene-tetracarbonyliron compounds containing Fe₂Sn₂ ring frameworks. Treatment of the dimers with strong donors results in ring fission leading to base-stabilized stannocene-tetracarbonyliron monomers.     

Iron(III) nitrate complexes with linear pentacoordinate ligands and their base hydrolysis products

The complexes, Fe(saldpt)NO₃, [Fe(salmedpt)]₂(NO₃)(OH), Fe(saldien)NO₃, and Fe(salmedien)NO₃·CH₂Cl₂, have been prepared. Solid state properties (IR spectra, Mössbauer spectra and magnetic moments) and solution properties (electronic spectra, PMR spectra, conductivities and cyclic voltammograms) have been measured. The saldpt and saldien compounds when reacted with aqueous KOH formed Fe(saldpt)sal and Fe(saldien)OC₂H₅·H₂O. Single crystals of Fe(saldpt)sal were prepared and examined. Crystal data: Fe(saldpt)sal: monoclinic, space group P2₁/c(#14), a=12.486(5), b=18.502(8), c=10.870(5) Å, β=104.23(3)°, V=2434(2) ų, Z=4, D_c=1.40 g cm⁻³, R=0.0473 (R_w=0.0681) for 317 parameters and 2107 data with F_o² > 3σ(F_o²).     

Protein dynamics: Mössbauer spectroscopy on deoxymyoglobin crystals

Mössbauer absorption experiments on ⁵⁷Fe of deoxygenated myoglobin crystals and on K₄⁵⁷Fe(CN)₆ dissolved in the water of metmyoglobin crystals were performed over a large temperature range. At low temperatures the mean square displacements, 〈x²〉, of the iron indicate solid-like behaviour of the whole system, whereas at higher temperatures protein-specific modes of motion contribute to 〈x²>. The protein dynamics are correlated with the mobility of the water within the protein crystals. A Brownian oscillator is used to model the protein-specific modes of motion measured at the ⁵⁷Fe nucleus. Three modes are necessary for understanding the Mössbauer spectrum. Two of them correspond to an extremely overdamped Brownian oscillator. The third mode can be understood as quasi-free diffusion. Whereas the protein molecule is frozen in conformational substates in the low temperature regime, it reaches transition states with a finite probability in the high temperature regime. The surface water mediates a possible trigger mechanism that switches on protein dynamics within a narrow temperature interval. Results from Mössbauer spectroscopy and from X-ray structure analysis are compared.     

Additional characterization of the two oxygen-containing compounds formed by the interaction of phthalocyaninatoiron(II) and dioxygen. Reproducible synthesis of the species isomorphic with the α form of Fe(II)Pc

The two compounds obtained by the interaction in solution of Fe(lI)Pc with O₂, presently considered two crystalline modifications of the μ-oxo dimer of Fe(III)Pc, are further characterized by visible absorption, XPS and Mössbauer spectra. The results stress the difference between the solid state properties of the two Fe(III) compounds.The behaviour of Fe(II)Pc and the two oxidized compounds in some chlorinated and non-chlorinated solvents, at different temperatures in the presence and absence of O₂, is reported. It is seen that heating the two Fe(III) products in 1-chloronaphthalene, or dimethylformamide, in vacuum sealed tubes, gives as a final product βFe(II)Pc. However, the same procedure in chlorobenzene or nitrobenzene yields, in a reproducible way, the pure oxygen-containing species which is isomorphic with αFe(II)Pc. Until now this product was only obtained in a fortuitous manner.     

Nature of iron deposits on the cardiac walls in β-thalassemia by Mössbauer spectroscopy

An identification of the nature and an estimation of the particle size distribution of the iron deposits on thalassemic heart tissue is carried out by variable temperature Mössbauer spectroscopy. Comparison of Mössbauer spectra obtained for the thalassemic heart tissue (I) with those of normal heart tissue (II) and of horse spleen ferritin (III) identifies the iron deposits to be small, superparamagnetic particles of ferritin and/or hemosiderin, two closely related iron storage proteins containing an iron core of (FeOOH)₈(FeO · OPO₃H₂). The dependence of the superparamagnetic relaxation time, τ₂, of magnetically ordered fine particles on their volume V via the magnetic anisotropy constant K of the material and the condition τ > τ_L, the Larmor precession time of the nuclear magnetic moment of ⁵⁷Fe about an effective magnetic field, for observation of hyperfine structure are used in analyzing the Mössbauer data to yield the particle size distribution. Particle diameters are estimated to be $\text{74 ± 12}\text{A}\text{?}$.     

Synthesis and structural studies by infrared and Mössbauer spectroscopy of adducts of tin(IV) and organotin(IV) derivatives with 2,2′-azopyridine

A number of complexes have been prepared by the reaction between 2,2′-azopyridine(AZP) and tin(IV) halides and organotin(IV) halides, and characterized by elemental analysis and infrared and variable temperature ¹¹⁹Sn Mössbauer spectroscopies. All of the new compounds have 1:1 stoichiometry, with the AZP ligand occupying two coordination sites by bonding through one of the ring and one of the azo group nitrogen atoms, to give rise to distorted octahedral structures. In the diorganotin complexes the two organic groups occupy trans positions. The infrared and Mössbauer spectroscopic data suggest that these compounds are monomeric in the solid state.     

Iron(III) complexes of N-donor ligands. Part II. The reaction of [Fe(L)2Cl2][FeCl4] with 1,2,4-triazole, 4-Allyl-1,2,4-triazole and 4,4′-bipyridyl; Rearrangement of the chelating ligands

[Fe(bpy)₂Cl₂][FeCl₄] and [Fe(dmbpy)₂Cl₂][FeCl₄] were reacted with 1,2,4-triazole (Htrz), 4-allyl-1,2,4,-triazole (Altrz) and 4,4′-bipyridyl (44bpy). The products obtained have been characterised by elemental analyses, infrared spectroscopy and Mössbauer spectroscopy. A rearrangement of the bipyridyl ligands was found and the products obtained are probably mononuclear for Htrz, dimeric for 44bpy and dimeric or polymeric for Altrz.     

119Sn Mössbauer spectroscopic studies of the products of the reaction of triorganotin(IV) derivatives with 6-thiopurine

A structural study of the products of the reaction of R₃Sn^IV derivatives (R = Me, Buⁿ, Ph) with 6-thiopurine, 6-TPH₂, and its sodium salt, 6-TPHNa, has been undertaken using Mössbauer spectroscopy and the point-charge model rationalization of the Mössbauer parameter nuclear quadrupole splitting. The synthetic reactions have been carried out at ca. 0 °C, 20 °C and 50 °C. The Mössbauer spectra of the complexes AlK₃Sn(6-TPH) are consistent with the occurrence of two distinct tin(IV) sites in samples prepared at the lower temperature, while one only site appears by increasing the temperature of the reaction. Two tin sites constantly occur in the products of the reactions involving the Ph₃Sn^IV moiety; the stoichiometry is assumed to be (Ph₃Sn)₃(6-TPH)(6-TP) for the uniquely-formed complex. Solid state polymeric structures with trigonal bipyramidal environments of the tin atoms and planar SnC₃ skeletons have been proposed. The apical ligand atoms have been assumed to be N, S and N, N in the samples showing two individual tin(IV) sites, and N, N when a single site was present.     

Complexes of chromium(II) and iron(II) with hexamethylphosphoramide

The chromium(II) complexes CrX₂(HMPA)₂, in which X = Cl or Br and HMPA is hexamethylphosphoramide, and Cr(HMPA)₄(BF₄)₂ have been prepared. The effective magnetic moments show little deviation from the value expected for high spin chromium(II) from room temperature to liquid nitrogen temperature. The diffuse reflectance spectra suggest that the chromium ions are in a strongly distorted six coordinate environment. The iron(II) complexes, FeX₂(HMPA)₂, X = Br or I, and [Fe(HMPA)_4](BF₄)₂, from their magnetic behaviour and Mössbauer and electronic spectra, contain tetrahedral iron(II). The isomer shift of the last complex is the most positive so far reported for a tetrahedral iron(II) complex.