The χT values (orange solid triangles) are also plotted in Figure . At room temperature it is 0.37 emu mol -1 K which is equivalent to χT = 0.375 emu mol -1 K for S = 1/2 and g = 2.0, i.e. the spin-only value expected for the independent paramagnetic Cu(II) ions. At lower temperatures, the value is reduced down to 0.053 emu mol -1 K at 2 K, indicating an antiferromagnetic exchange.