Generation of a Hetero Spin Complex from Iron(II) Iodide with Redox Active Acenaphthene-1,2-Diimine

The reaction of the redox active 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (dpp-BIAN) and iron(II) iodide in acetonitrile led to a new complex [(dpp-BIAN)FeIII2] (1). Molecular structure of 1 was determined by the single crystal X-ray diffraction analysis. The spin state of the iron cation in complex 1 at room temperature and the magnetic behavior of 1 in the temperature range of 2–300 K were studied using Mossbauer spectroscopy and magnetic susceptibility measurements, respectively. The neutral character of dpp-BIAN in 1 was confirmed by IR and UV spectroscopy. The electrochemistry of 1 was studied in solution and solid state using cyclic voltammetry. The generation of the radical anion form of the dpp-BIAN ligand upon reduction of 1 in a CH2Cl2 solution was monitored by EPR spectroscopy.

Interaction between Hemin and Prion Peptides: Binding, Oxidative Reactivity and Aggregation

We investigate the interaction of hemin with four fragments of prion protein (PrP) containing from one to four histidines (PrP106–114, PrP95–114, PrP84–114, PrP76–114) for its potential relevance to prion diseases and possibly traumatic brain injury. The binding properties of hemin-PrP complexes have been evaluated by UV–visible spectrophotometric titration. PrP peptides form a 1:1 adduct with hemin with affinity that increases with the number of histidines and length of the peptide; the following log K1 binding constants have been calculated: 6.48 for PrP76–114, 6.1 for PrP84–114, 4.80 for PrP95–114, whereas for PrP106–114, the interaction is too weak to allow a reliable binding constant calculation. These constants are similar to that of amyloid-β (Aβ) for hemin, and similarly to hemin-Aβ, PrP peptides tend to form a six-coordinated low-spin complex. However, the concomitant aggregation of PrP induced by hemin prevents calculation of the K2 binding constant. The turbidimetry analysis of [hemin-PrP76–114] shows that, once aggregated, this complex is scarcely soluble and undergoes precipitation. Finally, a detailed study of the peroxidase-like activity of [hemin-(PrP)] shows a moderate increase of the reactivity with respect to free hemin, but considering the activity over long time, as for neurodegenerative pathologies, it might contribute to neuronal oxidative stress.

Spin transition in a ferrous chloride complex supported by a pentapyridine ligand

Apparent high-spin complex with FeN5Cl coordination sphere exhibits a complete transition to the low-spin state on cooling.

Anion Influence on Spin State in Two Novel Fe(III) Compounds: [Fe(5F-sal2333)]X

Structural and magnetic data on two iron (III) complexes with a hexadentate Schiff base chelating ligand and Cl− or BPh4− counterions are reported. In the solid state, the Cl− complex [Fe(5F-sal2333)]Cl, 1, is high spin between 5–300 K while the BPh4− analogue [Fe(5F-sal2333)]BPh4, 2, is low spin between 5–250 K, with onset of a gradual and incomplete spin crossover on warming to room temperature. Structural investigation reveals different orientations of the hydrogen atoms on the secondary amine donors in the two salts of the [Fe(5F-sal2333)]+ cation: high spin complex [Fe(5F-sal2333)]Cl, 1, crystallizes with non-meso orientations while the spin crossover complex [Fe(5F-sal2333)]BPh4, 2, crystallizes with a combination of meso and non-meso orientations disordered over one crystallographic site. Variable temperature electronic absorption spectroscopy of methanolic solutions of 1 and 2 suggests that both are capable of spin state switching in the solution.

Crystal structure of bis(benzylamine-κN)[5,10,15,20-tetrakis(4-chlorophenyl)porphyrinato-κ4N]iron(II)n-hexane monosolvate

In the title compound, [FeII(C44H24Cl4N4)(C6H5CH2NH2)2]·C6H14or [FeII(TPP-Cl)(BzNH2)2]·n-hexane [where TPP-Cl and BzNH2are 5,10,15,20-tetrakis(4-chlorophenyl)porphyrinate and benzylamine ligands, respectively], the FeIIcation lies on an inversion centre and is octahedrally coordinated by the four pyrrole N atoms of the porphyrin ligand in the equatorial plane and by two amine N atoms of the benzylamine ligand in the axial sites. The crystal structure also contains one inversion-symmetricn-hexane solvent molecule per complex molecule. The average Fe—Npyrrolebond length [1.994 (3) Å] indicates a low-spin complex. The crystal packing is sustained by N—H...Cl and C—H...Cl hydrogen-bonding interactions and by C—H...π intermolecular interactions, leading to a three-dimensional network structure.

In air a spin crossover active iron(ii) complex of amine/NCBH3− ligands is converted to a low spin complex of imine/CN− ligands

A spin crossover FeII complex is in situ converted to a low spin complex in the presence of air, induced by the oxidative dehydrogenation of the tetradentate ligand and the generation of CN− from NCBH3−.