Linear-chain anti-ferromagnetism and spectroscopy of compounds CuX 2L 2, with x = CI, Br and L = substituted pyridine

Abstract

A series of linear-chain systems CuX 2L 2, with X= Cl, Br and L = substituted pyridine, is prepared and investigated. I.R., far-I.R., ligand-field and ESR spectra have been recorded; furthermore, magnetic susceptibility data at low temperatures are collected in order to find out the influence of small changes in the ligand molecule on the exchange constants. The chloride and bromide compounds of each ligand appear to be isomorphous according to the I.R. spectra, although small differences in the X-ray diffraction patterns occur. The M-X and M-L frequencies, which occur in the far-infrared region, have been assigned. The ESR parameters differ only slightly for the several chloride compounds, although the g-value of the 4-Etpy compound is less anisotropic than that of the others. All bromides have nearly the same ESR spectra. The susceptibility data of the compounds have been collected over the temperature region 4.2–80.0 K. J values for the compounds are calculated using the Heisenberg model for one-dimensional systems. The data do not agree with the Ising model. All compounds behave like antiferromagnetically-coupled copper ions bridged by halogen atoms. The J values correlate with a Cu-X frequency in the far-infrared. Examination of the exchange coupling constants reveals that the J values for the bromide compounds are consistently higher than those of the corresponding chlorides. Structural data show that the magnitude of exchange is influenced by the steric effects of the different ligands. For complete understanding of the factors influencing exchange coupling in these linear-chain systems, more detailed structural data are needed.