Syntheses and structural characterization of iron(II) coordination polymers with flexible 1,4-bis(imidazol-1-ylmethyl)benzene ligand

Iron(II) coordination polymers {[Fe(bix)2(NCS)2]·H2O}n (1) and [Fe(bix)2(N3)2]n (2) were synthesized using the flexible bidentate N-donor 1,4-bis(imidazol-1-ylmethyl)benzene (bix) ligand together with the mono-anionic ligands such as NCS− and N3− ions. In both of these complexes the iron(II) ion is in a distorted octahedral arrangement. Polymers 1 and 2, exhibit 2D framework with the ABCDE… and ABAB… packing modes, respectively. By considering the non-classical C–H⋯N hydrogen bonds, complex 2 is a three-dimensional polymer. Due to the presence of seven different kinds of trans-gauche conformations of the flexible bix ligands in the asymmetric unit of 1, there are four crystallographically independent iron(II) ions. In contrast to 1, in complex 2, all the bix ligands have the same conformation (trans-gauche). So, there is only one kind of iron(II) ion in this structure. Moreover, an attempted synthesis of [Fe(bix)3](ClO4)2 lead to the formation of unexpected diprotonated ionic species [bixH2](ClO4)2 (3) which was identified by X-ray analysis and infrared spectroscopy. Polymers 1 and 2 have been characterized by infrared spectroscopy, elemental and thermal analyses and single-crystal X-ray diffraction.