High-spin Sites Research Articles

Mössbauer spectroscopic studies on tetra(sulphonaphthyl)porphine iron(II) solutions

Mössbauer (78 K) and electronic absorption spectra (room temperature) of tetra(sulphonaphthyl)- porphine iron(II) solutions are reported and discussed. Evidence for only two iron(II) electronic environments, a low spin and a high spin site is found. The nature of each iron(II) environment is deduced with reference to previous work. The influence of the steric bulk of the meso substituents is discussed in comparison to similar studies on protoporphyrin IX iron(II) solutions and tetra( p-sulphophenyl)iron(II) solutions. The presence of the napthyl substituents on the methine carbons stabilises the low spin iron(II) species containing two axial water ligands.

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

AbstractThe 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 FeIII 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 FeIII atoms. The Mössbauer spectra are explained in terms of two FeIII high spin sites corresponding to trans‐ and cis‐positions in the structure.

Mössbauer studies of Fe2+ in anhydrous hemoglobin and its isolated subunits

The Mössbauer spectra of dehydrated αSH and βSH deoxyhemoglobin subunits were obtained over a temperature range from 77 to 200°K and compared with anhydrous hemoglobin spectra. The Mössbauer data for both subunits show a superposition of a ferrous high spin (S = 2) and a ferrous low spin (S = 0) quadrupole doublet of approximately equal intensity. No differences either in the isomer shifts or the quadrupole splittings were detected between the three hemoproteins. Consequently, the model for AHb–A with the α and β chains in different spin states proposed by previous investigators is probably incorrect. The observed quadrupole splittings, ΔEQ(T), are analyzed in a ligand field approximation, which gives the electronic structure of the low lying eigenstates of the ferrous ion at the two spin sites. The principal components of the EFG for the low and high spin iron sites calculated from the ligand field model are normal to the heme plane and have the values at T = 80°K of −0.09e 〈r−3〉 and 0.21e 〈r−3〉, respectively. At T = 80°K the asymmetry parameter, η, is zero for the low spin iron site and 0.39 for the high spin site. A possible interpretation of the origin of the spin state mixture based on the disruption of the hydrophobic interaction upon dehydration is discussed.