Magnetism of CuCl2·2D2O and CuCl2·2H2O, and of CuBr2·6H2O

The magnetic properties of little examined CuCl2·2D2O are studied and compared with those of CuCl2·2H2O. New CuBr2·6H2O is also examined. Susceptibility maxima appear for chlorides at 5.35 and 5.50 K, in the above order, with estimated antiferromagnetic ordering at 4.15 and 4.25 K. Curie-Weiss fits yield g of 2.210 and 2.205, and Weiss θ of −6.0 and −4.7 K, respectively, in χM = C/(T − θ). One-dimensional Heisenberg model fits to susceptibilities, including interchain exchange in a mean-field approximation, are performed. Interchain exchange is significant but much weaker than intrachain. The bromide hexahydrate strongly differs magnetically from any chloride hydrate, but exhibits notable similarities and differences compared to previously studied CuBr2. A broad susceptibility maximum occurs near 218 K, only 4% lower than for CuBr2, but with almost twice the magnitude. Powder X-ray diffraction data for CuBr2·6H2O may be best accounted for by a monoclinic unit cell that is metrically orthorhombic. The volume per formula unit is consistent with trends in metal ionic radii. However, an alternative monoclinic cell with 5% smaller volume more readily rationalizes the magnetism.