Autori: S. Tanase, P. Marques Gallego, E. Bouwman, G. J. Long, L. Rebbouh, F. Grandjean, R. de Gelder, I. Mutikainen, U. Turpeinen and J. Reedijk

Editorial: J. Chem. Soc. - Dalton Transaction, 13, p.1675-1684, 2006.

Rezumat:

The synthesis and characterization of two new iron(II) complexes, [Fe(pca)2(py)2]·py (1) and {[Fe(pca)2(H2O)]·H2O}n (2) and one new iron(III) complex, Na2{[Fe(pca)3)]2O}·2H2O·2CH3CN (3) (pca– stands for 2-pyrazinecarboxylate), are reported. Complex 1 is obtained from the reaction of iron powder with 2-pyrazinecarboxylic acid. The reaction of Fe(ClO4)3·10H2O with Hpca in the presence of 3 equiv. of Bu4NOH yields 2, whereas the presence of NaOH yields 3. The molecular structure of 1 contains an iron(II) ion with a pseudo-octahedral environment resulting from the coordination of two pca– ligands in a bidentate chelating fashion and two pyridine molecules; – stacking interactions between pyridine and pyrazine rings lead to a one-dimensional chain. Complex 2 is an iron(II) coordination polymer with an infinite zig–zag motif and an FeFe separation of 7.1 Å. In 2, the – stacking interactions involving the pyrazine rings and the strong hydrogen bonds between the coordinated water molecule and the carboxylate oxygens of two pca– ligands result in a three-dimensional network structure. Complex 3 consists of an anionic µ-oxo-bridged diiron(III) core with two crystallographically distinct iron(III) ions; the negative charge is compensated by two sodium cations. Complex 3 is assembled in a three dimensional network structure through coordination of Na(I) and hydrogen bond interactions. Temperature dependent magnetic susceptibility and Mössbauer spectroscopic studies indicate that 1 and 2 have similar magnetic properties. Both complexes are paramagnetic above 12 K, whereas antiferromagnetic ordering is observed below 12 K. The magnetic properties of 3 reveal strong intramolecular antiferromagnetic interactions between the two iron(III) ions with a J value of –221 cm–1; no long range intermolecular magnetic coupling is observed between 295 and 4.2 K.

Cuvinte cheie: iron, carboxylate, magnetic properties, Mossbauer