Synthesis, crystal structure and properties of tetrakis(pyridine-3-carbonitrile)dithiocyanatoiron(II) and of diaquabis(pyridine-3-carbonitrile)dithiocyanatoiron(II) pyridine-3-carbonitrile monosolvate

Abstract

The reaction of iron thiocyanate with 3-cyanopyridine (C6H4N2) leads to the formation of two compounds with the composition [Fe(NCS)2(C6H4N2)4] (1) and [Fe(NCS)2(C6H4N2)2(H2O)2]·2C6H4N2 (2). The asymmetric unit of 1 consists of one iron cation, two thiocyanate anions and four 3-cyanopyridine ligands in general positions. The iron cation is octahedrally coordinated by two N-bonded thiocyanate anions and four 3-cyanopyridine ligands. The complexes are arranged in columns along the crystallographic c-axis direction and are linked by weak C—H...N interactions. In 2, the asymmetric unit consists of one iron cation on a center of inversion as well as one thiocyanate anion, one 3-cyanopyridine ligand, one water ligand and one 3-cyanopyridine solvate molecule in general positions. The iron cation is octahedrally coordinated by two N-bonded thiocyanate anions, two cyanopyridine ligands and two water ligands. O—H...N and C—H...S hydrogen bonding is observed between the water ligands and the solvent 3-cyanopyridine molecules. In the crystal structure, alternating layers of the iron complexes and the solvated 3-cyanopyridine molecules are observed. Powder X-ray (PXRD) investigations reveal that both compounds were obtained as pure phases and from IR spectroscopic measurements conclusions on the coordination mode of the thiocanate anions and the cyanogroup were made. Thermogravimetric (TG) and differential thermoanalysis (DTA) of 1 indicate the formation of a compound with the composition {[Fe(NCS)2]3(C6H4N2)4} n that is isotypic to the corresponding Cd compound already reported in the literature. TG/DTA of 2 show several mass losses. The first mass loss corresponds to the removal of the two water ligands leading to the formation of 1, which transforms into {[Fe(NCS)2]3(C6H4N2)4} n , upon further heating.