Exchange Coupling in CuK2Cl4·2H2O by Paramagnetic Resonance Absorption

Cu${\mathrm{K}}_2$ ${\mathrm{Cl}}_4$·2${\mathrm{H}}_2$O contains two inequivalent ${\mathrm{Cu}}^{++}$ ions in each unit cell. At $\lambda =5.4\mathrm{}$ mm two peaks are obviously found corresponding to two different $g$ values, whereas only one peak is found at longer wavelengths. From these facts the exchange frequency between these dissimilar ions is estimated to be about 0.1 ${\mathrm{cm}}^{-1\mathrm{}}$. For the crystal orientation relative to the magnetic field at which the two types of ions are similar, the line width decreases with decreasing wavelength. This may be the result of the "$\frac{10}{3}$ effect" discussed by Anderson and Weiss.