Synthesis and Magnetic Properties of Solid Solutions of Ferromagnetic Layered Coordination Polymers Prepared from Solution and the Solid State

Reaction of mixtures of Co­(NCS)2 and Ni­(NCS)2 with ethylisonicotinate in EtOH in a ratio of 1:2 leads to the formation of solid solutions (mixed crystals) of the layered compound [Co x Ni1–x (NCS)2­(ethylisonicotinate)2] n that are always contaminated with an additional crystalline phase. Pure samples of the desired layer compound are accessible by using an excess of the metal salts, but in this case the Co content in the solid solutions, as determined by atomic absorption spectroscopy and energy dispersive X-ray spectroscopy, is always lower than that used in the synthesis. Therefore, solid solutions of Co x Ni1–x (NCS)2­(ethylisonicotinate)4 were synthesized that upon heating transform into solid solutions of the desired layered compound, and in this case the Co/Ni ratio exactly corresponds to that used in the synthesis. The formation of solid solutions of all compounds is already indicated by comparison of the experimental powder X-ray diffraction pattern of the solid solutions with that of physical mixtures with the same Co/Ni ratio. Magnetic and specific heat measurements reveal that the solid solutions show ferromagnetic ordering, as it is the case for the homometallic compounds reported recently, and that the magnetic ordering temperature increases linearly with increasing Ni content. AC measurements show that some Co/Ni inhomogeneity is present, which is more pronounced in the solid solutions prepared via the solid state than in those prepared from solution.