Synthesis, crystal structure and thermal decomposition pathway of bis(isoselenocyanato-κN)tetrakis(pyridine-κN)manganese(II)

Abstract

The reaction of MnCl2·2H2O with KSeCN and pyridine in water leads to the formation of the title complex, [Mn(NCSe)2(C5H5N)4], which is isotypic to its Fe, Co, Ni, Zn and Cd analogues. In its crystal structure, discrete complexes are observed that are located on centres of inversion. The Mn cations are octahedrally coordinated by four pyridine coligands and two selenocyanate anions that coordinate via the N atom to the metal centres to generate trans-MnN(s)2N(p)4 octahedra (s = selenocyanate and p = pyridine). In the extended structure, weak C—H...Se contacts are observed. Powder X-ray diffraction (PXRD) investigations prove that a pure sample was obtained and in the IR and Raman spectra, the C—N stretching vibrations are observed at 2058 and 2060 cm−1, respectively, in agreement with the terminal coordination of the selenocyanate anions. Thermogravimetric investigations reveal that the pyridine coligands are removed in two separate steps. In the first mass loss, a compound with the composition Mn(NCSe)2(C5H5N)2 is formed, whereas in the second mass loss, the remaining pyridine ligands are removed, which is superimposed with the decomposition of Mn(NCSe)2 formed after ligand removal. In the intermediate compound Mn(NCSe)2(C5H5N)2, the CN stretching vibration is observed at 2090 cm−1 in the Raman and at 2099 cm−1 in the IR spectra, indicating that the Mn cations are linked by μ-1,3-bridging anionic ligands. PXRD measurements show that a compound has formed that is of poor crystallinity. A comparison of the powder pattern with that calculated for the previously reported Cd(NCSe)2(C5H5N)2 indicates that these compounds are isotypic, which was proven by a Pawley fit.

Keywords

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