Magnetic resonance study of Rh complexes in AgCl microcrystals

X-ray or UV irradiation at room temperature of Rh3+ doped AgCl emulsion powders leads to the production of three paramagnetic Rh2+ related centres, labeled R4, R5 and R6. A combined X and Q band electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) study allowed the determination of a nearly complete structural model for these centres. In the X band ENDOR spectra of R4 and R5 interactions of the unpaired electron with nearby protons have been identified, indicating that for these centres Cl- ligands have been exchanged by H2O or OH-. The R6 centre, identified as a (RhCl6)4- complex, has been found to be fundamentally different from the dominant centre in large Rh2+ doped AgCl single crystals grown from the melt. The results are compared with recent work by other researchers in the same field.