Thermal decomposition reactions as tool for the synthesis of new metal thiocyanate diazine coordination polymers with cooperative magnetic phenomena.

Reaction of nickel thiocyanate with pyrimidine at room temperature leads to the formation of the new ligand-rich 1:2 (1:2 = ratio between metal and ligand) compound [Ni(NCS)(2)(pyrimidine)(2)](n) (2) which is isotypic to [Co(NCS)(2)(pyrimidine)(2)](n) (1) reported recently. In the crystal structure, the Ni(2+) ions are coordinated by four N atoms of pyrimidine ligands, which connect the metal centers into layers, and two N atoms of terminal bonded thiocyanato anions within slightly distorted octahedra. If the synthesis is performed under solvothermal conditions and an excess of the metal thiocyanate is used, single crystals of the ligand-deficient 1:1 compound [Ni(NCS)(2)(pyrimidine)](n) (4) are obtained. Investigations on the synthesis of this compound show that it is always contaminated with large amounts of the corresponding ligand-rich 1:2 compound 2. In the crystal structure, the Ni(2+) ions are coordinated by two N atoms of pyrimidine ligands, which connect the metal centers into chains, and two N atoms as well as two S atoms of mu-1,3 bridged thiocyanato anions, which conntect these chains into layers, within a slightly distorted octahedral geometry. On heating compounds 1 and 2 transform quantitatively into the ligand-deficient 1:1 Ni compound 4 and its isotypic Co compound 3. If nickel and cobalt thiocyanate are reacted with an excess of pyrimidine in a solvent-free reaction, discrete ligand-rich 1:4 complexes of composition [M(NCS)(2)(pyrimidine)(4)] (M = Co 5 and Ni 6) are obtained, which could be determined by single crystal structure analysis. In their crystal structure the metal ions are coordinated by four terminal bonded pyrimidine ligands and two terminal N-bonded thiocyanato anions. For the ligand-rich 1:2 and ligand-deficient 1:1 compounds magnetic measurements were performed, which reveal different magnetic properties: The 1:2 compounds show a ferromagnetic and the 1:1 compounds an antiferromagnetic ordering at lower temperatures.