SINGLE-CRYSTAL EPR STUDY OF THE COMPOUNDS [MCU(EDTA)(H2O)(3)]CENTER-DOT-H2O (M=SR, BA)

An EPR study of polycrystalline and single-crystal samples of compound s with formula [MCu(edta)(H2O)(3)].H2O (M = Sr, Ba) is reported. Only one exchange-narrowed line was observed for the two magnetically noneq uivalent copper ions in these lattices. The angular variation of its p osition 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(parallel to) = 2.34 8, g(perpendicular to) = 2.073, and g(parallel to) = 2.333, g(perpendi cular to) = 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 structur e 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 li neshapes.