Detection of charge compensating cation vacancies near Rh2+ complexes in AgCl and NaCl using Q-band ENDOR

Abstract

The effect of a charge compensating next nearest neighbour (nnn) cation vacancy on the electron nuclear double resonance (ENDOR) spectrum of a [RhCl₆]⁴⁻ complex in AgCl and NaCl single crystals is studied at Q-band. The Rh²⁺ ion has a low spin 4d⁷ ground state configuration and at low temperature, the complex undergoes an elongation along a crystal [001] direction (g_z axis). The unpaired electron strongly interacts with two equivalent Cl⁻ ions along the elongation axis. The electron nuclear double resonance spectrum of these axial Cl⁻ ions is clearly separated from all other interactions. The Q-band ENDOR analysis reveals a tilt in the (010) plane of the superhyperfine and quadrupole tensors for this interaction, due to the presence of the nnn cation vacancy on the axis. The tilt can be directly observed in the spectra through a splitting of the ENDOR transitions recorded in this plane and may be regarded as a fingerprint for the presence of the vacancy.