Features of Exchange Interaction Between Cr3+ Ions in Compounds [Fe(phen)3][Cr2(OH)(Ac)(nta)2]·6,25H2O and [Fe(bpy)3][Cr2(OH)(Ac)(nta)2]·8H2O

Resumo

Dimers of Cr³⁺ ions in compounds [Fe(phen)₃][Cr₂(OH)(Ac)(nta)₂]·6,25H₂O (I) and [Fe(bpy)₃][Cr₂(OH)(Ac)(nta)₂]·8H₂O (II), temperature dependences of the electron paramagnetic resonance (EPR) spectra of which in the range of 300–12 К are characteristic for dimers with strong antiferromagnetic exchange interaction are studied by the EPR method in the X-band. The anisotropy of the spin–spin interaction is estimated from fitting spectra corresponding to the multiplet with S = 2 to model spectra. It is shown that the tensor of the anisotropic spin–spin interaction considerably differs from that of the dipole–dipole contribution. Signals from the multiplet with S = 1 were also separated for the compound II that made it possible to estimate the fine structure parameter of the Cr³⁺ ion. Features of the variation of the integral intensity of EPR spectra are observed at temperatures below 6 К for I and 7 К for II, which are explained by the decrease in the value of the isotropic exchange between chromium ions in dimers. Only the intensity of spectrum changes and its shape is completely preserved.