E. Bill

Phenoxyl radical complexes of chromium(III)

The hexadentate ligand 1,4,7-tris(3-tert-butyl-5-methoxy-2-hydroxybenzyl)-1,4,7-triazacyclononane, H3L, forms a very stable neutral complex [CrIIIL]·2MeCN 2 with chromium(III) which undergoes electrochemically three one-electron oxidations to yield [CrIIIL]+, [CrIIIL]2+ and [CrIIIL]3+, respectively; these contain one, two and three coordinated phenoxyl radical ligands; [CrIIIL]·2MeCN and [CrIIIL]ClO4·3MeCN are characterized by X-ray crystallography.

Mössbauer study of a novel binuclear Fe(II/III) delocalized-valence compound

In this paper, we briefly summarize the main conclusions of the Mössbauer analysis of [L2Fe2(μ-OH)3] (ClO4)2·2CH3OH·2H2O with L=N,N,N-trimethyl-1,4,7-triazacyclononane, a novel dimeric iron compound, which possesses a central exchange-coupled delocalized-valence Fe(II/III) unit. The complete delocalization of the excess electron in the dimeric iron center is concluded from the indistinguishability of the two iron sites in Mössbauer spectroscopy. The magnetic Mössbauer spectra imply a system spinSt=9/2 for the dimer in its ground state. The values for hyperfine and spin-Hamiltonian parameters, obtained from simulations of the Mössbauer spectra, are δ=0.74 mms−1, ΔEQ=−2.14 mms−1,A⊥=−10.6 T,A∥=−13.5 T andD=1.8 cm−1. The system spinSt=9/2 is interpreted to be a consequence of double-exchange coupling.

Mössbauer and EPR study of nitrosyl hemoglobin

Nitrosyl hemoglobin was prepared by bubbling fresh57Fe-enriched rat hemoglobin with NO. S- and X-band EPR spectra at 77 K are typical for anS=1/2 system with an anisotropicg-tensor and exhibit hyperfine interactions of14N with the electronic spin. Mössbauer spectra at 4.2 and 100 K consist of a superposition of spectra from high- and low-spin Fe(III), deoxygenated hemoglobin and a component corresponding toS=1/2,g=2, hyperfine constantsAxx/gnΒn=Ayy/gnΒn=−19.6 T,Azz/gnΒn=6.8 T, quadrupole splitting δEQ=1.5 mm s−1, isomer shiftIs=0.42 mm s−1 and linewidth 0.4 mm s−1. The spin-lattice relaxation rate at 100 K is <2×106 s−1.

Exchange interaction in trinuclear transition-metal complexes

Heterotrinuclear transition-metal complexes are of interest for the study of long-range magnetic interactions and as model compounds for the investigation of biological electron transport chains. The systems under study here contain paramagnetic Fe111-containing terminal units and a bridging unit with M11=Zn, Cu, Ni, Co, Fe, Mn. The spectroscopic methods applied include Mössbauer, — EPR- and magnetic susceptibility investigations. The spin-Hamiltonian analysis of the measured results yields information about the intramolecular super-exchange interactions among the various magnetic transmition-metal sites. In view of the 7Å separation between the two terminal Fe111 sites, the Fe111...Fe111 exchange coupling of the order −10cm−1 is large.

Cubic symmetry around iron in CoSi2

The Mössbauer spectra of 57Fe in CoSi2 have been measured in 3.5 and 4.0 T external magnetic fields. The measured spectra showed only magnetic splitting thereby proving the cubic symmetry around 57Fe atoms in CoSi2 (fluorite‐type lattice). Two iron positions were found: in one the iron atoms substitute Co atoms, in the other one the iron populates the empty cubic site in the lattice. It is considered that the results may well contribute to clarifying the atomic positions and local symmetries in metastable Co‐ and Fe‐silicides forming after implantation of Co and Fe in Si at elevated temperatures.

Mössbauer study of iron-doped lithium niobate

From Mössbauer spectra of LiNbO3∶57Fe(III) single crystals under external fields of 4.92 and 6.2 T, the crystal field and hyperfine parameters are determined. Transmission integral fits indicate a Boltzmann population of the Fe(III) electronic levels with a spin temperature equal to the sample temperature. Spectra at external fields of 0 T and 19 mT can be satisfactorily simulated using an effective spin 1/2,g-factors calculated from spin-expectation values and an internal averaged dipole field of 5.5 mT inclined 20‡ to thec-axis. The simulations indicate cross-relaxation between Nb and Li nuclear spins and the Fe(III) electronic spin.