Electron paramagnetic resonance, electron nuclear double resonance, and electron spin echo envelope modulation of Fe(CN)3−6 in a KCl lattice

Abstract

An electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), and electron spin echo envelope modulation (ESEEM) study has been carried out on Fe(CN)3−6 in a KCl lattice. The EPR spectrum showed the formation of a large number of centers, which correspond to different configurations of the charge compensating cation vacancies. The two major centers called center Ia and Ib have been well characterized. Both centers have orthorhombic symmetry and show a large g anisotropy. The principle g values are: gx =2.079, gy =3.054, and gz =0.400 for center Ia; gx =2.007, gy =3.177, and gz =0.752 for center Ib. The ligand field splitting and the orbital reduction factor k have been obtained through analyzing the spectra in terms of the generalized spin Hamiltonian. A number of unusual features observed in the EPR spectra have been found to be due to the high level of g anisotropy. The ENDOR and ESEEM measurements performed on center Ia revealed nearly all the coupling tensors between the unpaired electron and the 13C and 14N nuclei. The principle values and tensor orientations were precisely determined by least-squares fitting. The orientations of the coupling tensors give a detailed picture of the complex under the influence of the two cation vacancies. The coupling constants of 13C were found to be an order of magnitude larger than those of 14N. Level anticrossing was observed for the nuclear spin states of 14N.