Photoinduced phenomena and structural analysis associated with the spin-state switching in the [FeII(DPEA)(NCS)2] complex

International audienceOut-of-equilibrium photoinduced switching from the low-spin to the high-spin state has been investigated on the iron(II) complex [Fe(II)(DPEA)(NCS)2] by both optical reflectivity and magnetic measurements under continuous light irradiation at low temperature. The photoinduced HS state can be observed up to 47 K and the relaxation process has been followed. Structural changes of both the temperature- and the photoinduced spin-state switching have been analyzed in detail by x-ray diffraction indicating no change of symmetry. Short intermolecular contacts and intramolecular deformations associated with the change of molecular spin state have been quantified. Actually a crossover behavior is observed at thermal equilibrium with however a quasiabrupt shape indicating significant cooperative effects. These aspects are compared between the temperature- and photoinduced spin crossovers

OXIDATIVE STRESS BIOMARKERS IN MUSSELS SAMPLED FROM FOUR SITES ALONG THE MOROCCAN ATLANTIC COAST (BIG CASABLANCA)

Catalase (CAT) activity and malondialdehyde (MDA) level in whole bodies of the mussel perna perna, collected from four stations along the Moroccan Atlantic coast (Big Casablanca area), were monitored to evaluate stress effects on mussels collected from the selected sites. The oxidative stress biomarkers showed statistically significant differences at the polluted sites when compared to the control ones. In general, our data indicated that CAT activity and MDA concentration are a higher and significant (p < 0.05) in mussels collected at polluted site when compared to specimen sampled from control ones. In conclusion, the oxidative stress biomarkers response obtained for October 2010 and 2011, clearly demonstrate the potential presence of different contaminants in Site 4 and Site 3 reflecting the intensity of pollution in these areas

Remarkable steric effects and influence of monodentate axial ligands L on the spin-crossover properties of trans-[FeII(N4 ligand)L] complexes

Iron(II) complexes obtained from tetradentate, rigid, linear N4 ligands have been investigated to appraise the influence of steric effects and the impact of trans-coordinated anions on the spin-transition behavior. .

Thermal and light-induced spin-transitions in iron(II) complexes of 2,6-bis(4-halopyrazolyl)pyridines: the influence of polymorphism on a spin-crossover compound

The syntheses of 2,6-bis(4-chloropyrazol-1-yl)pyridine (L1), 2,6-bis(4-bromopyrazol-1-yl)pyridine (L2) and 2,6-bis(4-iodopyrazol-1-yl)pyridine (L3) by electrophilic halogenation of 2,6-bis(pyrazol-1-yl)pyridine are reported. The complex [Fe(L1)2][BF4]2 crystallises in two different solvent-free polymorphs. The tetragonal (alpha) form crystallises in a known version of the "terpyridine embrace" structure, and undergoes an abrupt spin-transition at 202 K. The orthorhombic (beta) form exhibits a modified form of the same packing motif, containing two unique iron sites in a 2 : 1 ratio. One-third of the complex molecules in that material undergo a very gradual thermal spin-crossover centred at 137 K. Comparison of the two structures implies that spin-crossover cooperativity in the alpha-polymorph is transmitted in two dimensions within the extended lattice. [Fe(L2)2][BF4]2 is isostructural with alpha-[Fe(L1)2][BF4]2 and exhibits a similarly abrupt spin-transition at 253 K. In contrast, [Fe(L3)2][BF4]2 is low-spin as a powder at 360 K and below and can be crystallised as two different solvates from acetone solution. All three compounds exhibit the LIESST effect at 10 K, with photoconversions of 40-100%. Their LIESST relaxation temperatures obey the empirical T(LIESST) = T0- 0.3T(1/2) (T0 = 150 K) law that we have previously proposed for this class of compound

Thermal and light-induced spin-crossover in salts of the heptadentate complex [tris(4-{pyrazol-3-yl}-3-aza-3-butenyl)amine]iron(II)

The syntheses of [FeL][BF4]2·H2O, [FeL][ClO4]2·H2O, [FeL][NO3]2·CH3NO2 and [FeL][CF3SO3]2 (L = tris(4-{pyrazol-3-yl}-3-aza-3-butenyl)amine) are described. The isostructural BF4– and ClO4– salts are high-spin between 5–300 K, while the other two compounds are high-spin at room temperature but undergo gradual high -> low spin transitions upon cooling. For [FeL][NO3]2 this transition is centred at 139 K and proceeds to near-completeness, while for [FeL][CF3SO3]2 it is centred at 144 K and only proceeds to 50% conversion..