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 (1), [(Co­(NCS)2]2(4-ethylpyridine)6 (2), and [Co­(NCS)2(4-ethylpyridine)2]n (3). In all compounds
the coordination of the Co­(II) ions is distorted octahedral. 1 consists of discrete monomeric complexes and in 2 two Co­(II) cations are linked by pairs of μ-1,3-bridging thiocyanato
ligands into dimers. In the crystal structure of 3 the
Co­(II) cations are connected into chains by the same bridge as in 2. Magnetic studies show that 1 and 2 are paramagnets down to a temperature of 2 K, while compound 3, which is the main object of this study, is an antiferromagnet
with the Néel temperature TN =
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 3 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.