EPR studies of Rh and Rh(II) centers stabilized in NH4Cl single crystals

Abstract

The electron paramagnetic resonance (EPR) studies of gamma irradiated ammonium chloride single crystals doped with rhodium have given evidence to suggest the stabilization of Rh0 and Rh(II) at interstitial sites in a compressed octahedral coordination with D4h symmetry. The EPR spectrum of Rh0 has been found to be highly temperature dependent, the intensity increasing with the lowering of temperature and was observable only below −100 °C. Well resolved hyperfine structure due to 103Rh has been observed for Rh0 center. Its g values suggest that the unpaired electron is in a pure ‖3z2−r2〉 orbital, in contrast to the ‖x2−y2〉 character of the unpaired electron of Rh(II) center. At 77 °K superhyperfine structure due to four equivalent chlorines was observed in the EPR spectrum of Rh(II) center, indicating the overlap of ‖x2−y2〉 orbital with the equatorial ligands.