Synthesis, crystal structure and properties of bis(isoselenocyanato-κN)tetrakis(pyridine-κN)nickel(II)

Abstract

The reaction of nickel chloride hexahydrate with potassium selenocyanate and pyridine in water leads to the formation of crystals of the title complex, [Ni(NCSe)2(C5H5N)4], which were characterized by single-crystal X-ray diffraction. Its crystal structure consists of discrete complexes, located on centers of inversion, in which the Ni cations are sixfold coordinated by two terminal N-bonded selenocyanate anions and four pyridine ligands within a slightly distorted octahedral coordination. In the crystal, the complexes are connected by weak C—H...Se interactions. PXRD investigations revealed that a pure crystalline phase has formed. In the IR and Raman spectra, the C—N stretching vibrations are observed at 2083 and 2079 cm−1, respectively, in agreement with the presence of only terminally bonded anionic ligands. Upon heating, one well-resolved mass loss is observed, in which two of the four pyridine ligands are removed, leading to a compound with the composition Ni(NCSe)2(C5H5N)2. In this compound, the C—N stretching vibration is shifted to 2108 cm−1 (Raman) and 2115 cm−1 (IR), indicating the presence of μ-1,3-bridging anionic ligands. In its PXRD pattern, very broad reflections are observed, indicating for poor crystallinity and/or very small particle size. This crystalline phase is not isotypic to its Co and Fe analogs.

Keywords

• crystal structure
• nickel selenocyanate
• discrete complex
• thermal properties