Metal-Dependent Antiferromagnetic Interactions in Ba2MCl6 (M2+ = Co, Fe, Mn)

Exploring the wide array of metal-halide structures offers the opportunity for examining structure–property relationships in magnetic solids. Here, we report the magnetism of Ba2CoCl6, which has a crystal structure based on edge-sharing octahedral transition-metal-halide dimers. Furthermore, the previously unreported analogues Ba2FeCl6, Ba2MnCl6, and Ba2MgCl6 are synthesized and their structures are determined by single-crystal X-ray diffraction. Using Ba2MgCl6 as a diamagnetic control, we measure their temperature-dependent magnetizations and heat capacities. Ba2CoCl6 and Ba2FeCl6 exhibit short-range antiferromagnetic ordering near 1 K, while Ba2MnCl6 displays a transition to long-range magnetic ordering at 0.63 K that is not observed down to 0.5 K in Ba2CoCl6 and Ba2FeCl6. We conclude that the short-range intradimer and long-range interdimer magnetic ordering temperatures depend on both the ionic radius and electronic configuration of the transition metal.