Versatility in the Binding of 2-pyrazinecarboxylate with Iron. Synthesis, Structure and Magnetic Properties of Iron(II) and Iron(III) Complexes


The synthesis and characterization of two new iron(ii) complexes, [Fe(pca)2(py)2]·py (1) and [Fe(pca) 2(H2O)]·H2On (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(ClO 4)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; π-π 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 Fe⋯Fe separation of 7.1 Å. In 2, the π-π 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 -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. © The Royal Society of Chemistry 2006.



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