Magnetic interactions in homometallic chains M(4-cyanopyridine)2Cl2, M=Cu,Ni,Co

Abstract

The title compounds have been synthesized for the first time. The crystal structure of the copper compound has been determined to consist of chloride bibridged chains of copper ions with the 4-cyanopyridine (4-CNPy) ligands coordinated to the metal ions through the pyridine nitrogens in the axial sites. Chemical and powder x-ray analysis indicate that the compounds form an isostructural series. The powder susceptibilities have been measured between 2 and 300 K. Effects of either antiferromagnetic exchange (Cu) or ferromagnetic exchange (Ni,Co) within the chains have been seen. The copper data has been fit to the model of a S=1/2 Heisenberg antiferromagnetic linear chain with exchange constant J/k=−13.7(2) K. The nickel data has been fit to the model of a S=1 ferromagnetic Heisenberg linear chain with exchange constant J/k=+4.8(2) K. The cobalt data has been fit to the model of a S=1/2 ferromagnetic Ising linear chain with exchange constant J/k=+6.6(2) K. The Ni and Co compounds order antiferromagnetically at 7.2(2) and 2.1(2) K, respectively. Magnetic-field-induced phase transitions have been observed in the Ni and Co compounds. The critical fields extrapolated to T=0 are Hc=4.2(2) kOe and Hc=1.4(2) kOe for the Ni and Co compounds, respectively.