The influence of ClO4- and PF6- anions and the steric hindrance of flexible bis-imidazole ligands on the formation and structures of iron(II) coordination polymers

Abstract

Treatments of the flexible 1,4-bis(imidazolyl)butane (bib) ligand with Fe(II) salts in a mixture of ethanol and water (1:1) as a solvent at room temperature resulted in the formation of two novel coordination polymers, {[Fe(bib)3](ClO4)2}n (1) and {[Fe(bib)3](PF6)2}n (2), with two distinctly different network structures due to the variation of the ClO 4- and PF6- moieties in these compounds. Their infrared spectra, X-ray powder diffraction (XRPD), elemental and thermal analyses were also investigated in detail. The results of the X-ray analyses demonstrate that in these structures, the iron(II) ion lies on an inversion center and adopts an FeN6 octahedral geometry. Each μ2-bib serves as a bridging ligand connecting two adjacent iron(II) ions. In the structure of 1, six μ2-bib ligands are simultaneously coordinated to one central iron(II) ion to form an open 3D 2-fold interpenetrating framework with an α-polonium (pcu) topology, while 2 has an open 3D network with an acs [point symbol (49.66)] structure. The structure of [bibMeH](PF6) [bib Me = 1,4-bis(2-methylimidazolyl)butane] (3) has also been studied by X-ray crystallography as an unexpected product in an attempt to synthesize the {[Fe(bibMe)3]2+}n cation with the PF6- anion. © 2013 Published by Elsevier Ltd.