Impurity-ligand distances derived from magnetic resonance and optical parameters

Abstract

Non empirical methods for obtaining information from EPR, ENDOR and optical data on the true impurity-ligand distance,R, as well as on the true variations, ΔR, induced by chemical and hydrostatic pressures, phase transitions in the host material and temperature changes are discussed through this work. Special attention is addressed to spectroscopic parameters of d-impurities whose dependence onR can reasonably be calculated theoretically for the superhyperfine (shf) tensor or the lowest optical transitions but not for fine structure terms. In the case of impurities with unpaired σ-electrons it is shown that the isotropic shf constant,A s, is specially sensitive toR changes. The microscopic origin of this fact is discussed in detail. Determination of trueR values from experimentalA s has been carried out for impurities like Mn2+ or Ni+ with encouraging results. In the case of Mn2+ in fluorides, results obtained by this method coincide with those reached through EXAFS and the analysis of the experimental 10 Dq. Finally, for some selected complexes, a view is offered on the dependence of several EPR and optical parameters upon metal-ligand distances. The main conclusion is that ΔR values of the order of 0.1 pm can be detected using EPR and optical parameters thus improving by an order of magnitude the sensitivity reached through EXAFS. In particular the use of ENDOR allows one to measure ΔR values close to 0.01 pm.