ENDOR identification of a Rh+ centre in solution-grown NaCl

Abstract

X-Irradiation at room temperature produces three stable rhodium-related centres in solution-grown NaCl doped with Rh³⁺. Two have earlier been identified as Rh²⁺-centred complexes. The third centre, which could only be observed with electron nuclear double resonance (ENDOR), appeared to have cubic symmetry. In the present work this centre is identified as a (RhCl₆)^5- complex, substituting for (NaCl₆)^5-. The central Rh⁺ ion has a 4 configuration, leading to a centre with effective spin S=1. This is confirmed experimentally by the occurrence of a ΔM_S=2 transition in the EPR spectrum. Interactions of the unpaired electrons with the central Rh nucleus, the first-shell CI and the fourth-shell Na nuclei are observed in the ENDOR spectrum. The angular dependence of these interactions shows that the centre has cubic symmetry. The spin Hamiltonian parameters obtained are used to estimate the crystal field splitting and the unpaired spin density over the complex.