Versatility in the binding of 2-pyrazinecarboxylate with iron. Synthesis, structure and magnetic properties of iron(II) and iron(III) complexes

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Publication year
2006Source
Dalton Transactions, 13, (2006), pp. 1675-1684ISSN
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Article / Letter to editor

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Organization
Solid State Chemistry
Journal title
Dalton Transactions
Issue
iss. 13
Page start
p. 1675
Page end
p. 1684
Subject
Molecular MaterialsAbstract
The synthesis and characterization of two new iron(II) complexes, [Fe(pca)(2)(py)(2)]center dot py (1) and {[Fe(pca)(2)(H2O))] center dot H2O}(n) (2) and one new iron(m) complex, Na-2{[Fe(pca)(3))](2)O}center dot 2H(2)O center dot 2CH(3)CN (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)center dot 10H(2)O 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 ail 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; pi-pi stacking interactions between pyridine and pyrazine rings lead to a one-dimensional chain. Complex 2 is ail iron(II) coordination polymer with an infinite zig-zag motif and an Fe center dot center dot center dot Fe separation of 7. 1 angstrom. In 2, the pi-pi 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 mu-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 Mossbauer 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.
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