Structural and Magnetic Studies of a New Co(II) Thiocyanato
Coordination Polymer Showing Slow Magnetic Relaxations and a Metamagnetic
Transition
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Abstract
Reaction
of Co(NCS)<sub>2</sub> with 4-ethylpyridine leads to the formation
of three new compounds of composition Co(NCS)<sub>2</sub>(4-ethylpyridine)<sub>4</sub> (<b>1</b>), [(Co(NCS)<sub>2</sub>]<sub>2</sub>(4-ethylpyridine)<sub>6</sub> (<b>2</b>), and [Co(NCS)<sub>2</sub>(4-ethylpyridine)<sub>2</sub>]<sub><i>n</i></sub> (<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><sub>N</sub> =
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