Thermal decomposition reactions as an alternative tool for the preparation of new coordination polymers: synthesis, crystal structure, thermal and magnetic properties of poly[bis(thiocyanato-N)-bis(μ2-pyrazine-N,N')-manganese(II)] and poly[bis(μ2-thiocyanato-N,S)-(μ2-pyrazine-N,N'-manganese(II)]

Reaction of manganese thiocyanate with pyrazine in acetonitrile leads to the formation of the two new coordination polymers poly[bis(thiocyanato-N)-bis(μ2-pyrazine-N,N')-manganese(II)] (I) and poly[bis(μ2-thiocyanato-N,S)-(μ2-pyrazine-N,N'-manganese(II)] (II). Whereas I can be prepared in large amounts and very pure in solution, II is always obtained as mixtures of compound I and II. In the crystal structure of compound I the manganese centers are octahedral surrounded by four pyrazine ligands and two nitrogen atoms of two thiocyanate anions. The manganese centers are connected by the pyrazine ligands via μ-N,N' coordination forming layers which are parallel to (001). In the crystal structure of the amine poorer compound II the manganese atoms are surrounded by two pyrazine ligands, two nitrogen atoms and two sulfur atoms of four thiocyanate anions. The manganese centers are connected by the thiocyanate anions via μ-N,S coordination forming layers which are parallel to (100). On heating compound I looses half of the pyrazine ligands forming the amine poorer compound II. Magnetic measurements reveal that compound I exhibits only weak antiferromagnetic interactions, whereas the latter shows antiferromagnetic ordering at about 26 K which is mediated by the thiocyanate anions