Structural and Magnetic Studies of a New Co(II) Thiocyanato Coordination Polymer Showing Slow Magnetic Relaxations and a Metamagnetic Transition

Reaction of Co­(NCS)₂ with 4-ethylpyridine leads to the formation of three new compounds of composition Co­(NCS)₂(4-ethylpyridine)₄ (<b>1</b>), [(Co­(NCS)₂]₂(4-ethylpyridine)₆ (<b>2</b>), and [Co­(NCS)₂(4-ethylpyridine)₂]_<i>n</i> (<b>3</b>). In all compounds the coordination of the Co­(II) ions is distorted octahedral. <b>1</b> consists of discrete monomeric complexes and in <b>2</b> two Co­(II) cations are linked by pairs of μ-1,3-bridging thiocyanato ligands into dimers. In the crystal structure of <b>3</b> the Co­(II) cations are connected into chains by the same bridge as in <b>2</b>. Magnetic studies show that <b>1</b> and <b>2</b> are paramagnets down to a temperature of 2 K, while compound <b>3</b>, which is the main object of this study, is an antiferromagnet with the Néel temperature <i>T</i>_N = 3.4 K. Its magnetic structure is built from ferromagnetic chains, which are weakly antiferromagnetically coupled. With increasing magnetic field a metamagnetic transition starts at ∼175 Oe, as observed for a polycrystalline sample. Magnetic relaxations, which were observed in the antiferromagnetic state, are retained at the metamagnetic transition. With decreasing field <b>3</b> remains in a state, in which except of the faster magnetic relaxation process in single chains also a slower process coexists resulting in the appearance of a magnetic hysteresis loop