Cobalt(ii) octacyanotungstate(v) organic–inorganic hybrid ferromagnetic materials with pyrazine and 4,4′-bipyridine

Abstract

Two new ferromagnetic organic–inorganic hybrid materials {Co^II₃(H₂O)₆(pyz)₃[W^V(CN)₈]₂}·3.5H₂O (1) and {Co^II₃(H₂O)₄(4,4′-bpy)₃[W^V(CN)₈]₂}·1.5(4,4′-bpy)·6H₂O (2) have been synthesised and characterised. The structure of the compounds have been investigated combining EXAFS (extended X-ray absorption fine structure), ES-MS (electrospray mass spectrometry), IR (infrared spectroscopy), UV-VIS electronic spectroscopy and TGA (thermogravimetric analysis) coupled with QMS (quadrupole mass spectrometer) experiments. The studies reveal that both compounds consist of Co^II–NC–W^V and Co^II–L–Co^II linkages (L = pyrazine (1) or 4,4′-bipyridine (2)). Both networks are created by cyano-bridged Co^II₃W^V₂ chains joined by organic linkers into a 2D architecture. A difference of cobalt coordination numbers in both compounds derived from EXAFS study is consistent with the ES-MS conclusion. The ac magnetic characterisation exhibits the transition to the ferromagnetic phase at T_C = 26 K (1) and to the spin glass-like phase at T_G = 16 K (2). The frequency dependent χ′(T) and χ″(T) signals indicate the presence of some disorder in spin alignment below ordering temperatures. Both networks are also characterised a by magnetic hysteresis loop of coercive field H_c = 750 Oe (1) and 1200 Oe (2) at T = 4.2 K.