Electron Paramagnetic Resonance of Electron Irradiated K3Rh(CN)6 in a KCl Lattice

Electron irradiation of the diamagnetic Rh(CN)₆³⁻ ion in a KCl host lattice produces three paramagnetic species. EPR studies reveal that one of the species can be assigned as Rh(CN)₄Cl₂⁴⁻, of $D_{\text{4h}}$ symmetry, ${\text{4d}}^7$ low spin configuration, arising from the trapping of an electron in a $d_z^2$ orbital followed by the substitution of two axial cyanides by chloride ions. The experimental data have been interpreted in terms of a spin Hamiltonian yielding the principal values of the $g$ and hyperfine tensors as $g_{\Vert }{\text{\hspace{0.17em}=\hspace{0.17em}1.995, g⊥\hspace{0.17em}=\hspace{0.17em}2.297, A}}_{\Vert }^{\mathrm{Rh}}{\text{\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}40.8\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−4}}{\mathrm{cm}}^{\text{−1}}{\mathrm{,\; A\perp }}^{\mathrm{Rh}}{\text{\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}36.9\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−4}}{\mathrm{cm}}^{\text{−1}}{\mathrm{,\; A}}_{\Vert }^{\mathrm{Cl}}{\text{\hspace{0.17em}=\hspace{0.17em}+\hspace{0.17em}27.8\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−4}}{\mathrm{cm}}^{\text{−1}}{\mathrm{,\; A\perp }}^{\mathrm{Cl}}{\text{\hspace{0.17em}=\hspace{0.17em}+\hspace{0.17em}12.4\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−4}}{\mathrm{cm}}^{\text{−1}}$ . Theoretical estimates of $g$ values confirm this assignment. A semiempirical estimate of the unpaired electron density on the metal and ligands is presented.