Single-crystal EPR study of the compounds [MCu(edta)(H2O)3]·H2O (M = Sr, Ba)

Abstract

An EPR study of polycrystalline and single-crystal samples of compounds with formula [MCu(edta)(H₂O)₃]·H₂O (M = Sr, Ba) is reported. Only one exchange-narrowed line was observed for the two magnetically non-equivalent copper ions in these lattices. The angular variation of its position was measured in three perpendicular planes. The data were used to obtain the crystal and molecular g-tensors, and the orientation of the molecules within the unit cell. We obtained g_∥= 2.348, g⊥= 2.073, and g_∥= 2.333, g⊥= 2.079 for the principal values of the molecular g-tensors of each copper ion in the strontium and barium compounds, respectively. These values reflect the axially elongated topology presented by the [CuN₂O₄] octahedra. Strontium and barium substitution in the structure causes only a slight variation of the distances and angles involved in the superexchange pathways. However, owing to the magnitude of the exchange couplings, this fact produces important changes in the EPR lineshapes.