Synthesis, Crystal Structure, and Thermal, Magnetic and Spectroscopic Properties of New Thiocyanato Transition Metal Coordination Polymers Based on Pyrimidine as Ligand

Reaction of manganese and iron thiocyanate with pyrimidine in solution at room temperature leads to the formation of the isotypic new ligand-rich 1:2 (1:2 = ratio between metal and ligand) compounds [Mn(NCS)(2)(pyrimidine)(2)](n) (1) and [Fe(NCS)(2)(pyrimidine)(2)](n) (2). Their crystal structures were determined by single crystal X-ray analysis. The metal cations are coordinated by four pyrimidine ligands, which connect them into layers, and two terminal N-bonded thiocyanato anions in a distorted octahedral arrangement. Investigations on their thermal behavior show that the complexes decompose quantitatively into the ligand-deficient 1:1 compounds [Mn(NCS)(2)(pyrimidine)](n) (3) and [Fe(NCS)(2)(pyrimidine)](n) (4). It must be noted that they can only be prepared by thermal decomposition of their ligand-rich 1:2 precursor compounds, whereas a synthesis in solution is not possible. In comparison with the structure of their 1:2 precursors, the thiocyanato anions become mu-1,3 bridging, which was proved by X-ray powder diffraction and spectroscopic investigations. Magnetic measurements of the ligand-rich and -deficient compounds reveal similar behavior with an antiferromagnetic ordering at lower temperatures, which in the case of the ligand-rich compounds must be mediated by the aromatic pi-system of the pyrimidine ligands.