Investigating the effect of flexible ligands on the crystal engineering of the iron(II) coordination compounds

Iron(II) coordination compounds [Fe(bib)2(NCS)2]n (1) and [Fe(bpp)(NCS)2] (2) were synthesized by using the neutral flexible bidentate N-donor ligands 1,4-bis(imidazolyl)butane (bib) and 1,3-bis(3,5-dimethylpyrazolyl)propane (bpp), mono-anionic NCS− ligand and appropriate iron(II) salts. In the CdSO4 network structure of 1, the iron(II) ion lies on an inversion center and exhibits an FeN6 octahedral arrangement while, in the monomeric structure of 2, the iron(II) ion adopts an FeN4 tetrahedral geometry. In the complex 1, each μ2-bib acts as bridging ligand connecting two adjacent iron(II) ions while in the complex 2, the bpp ligand is coordinated to an iron(II) ion in a cyclic-bidentate fashion forming an eight-membered metallocyclic ring. Coordination compounds 1 and 2 have been characterized by infrared spectroscopy, elemental analyses and single-crystal X-ray diffraction. Thermal analysis of polymer 1 was also studied. An attempt to synthesize [Fe(bbd)(NCS)2] (3) (bbd = 1,4-bis(3,5-dimethylpyrazolyl)butane) with the reaction of bbd, Fe(NH4)2(SO4)2·6H2O and KNCS was failed.