Metal–Metal Interactions in Trinuclear Copper(II) Complexes [Cu3(RCOO)4(H2TEA)2] and Binuclear [Cu2(RCOO)2(H2TEA)2]. Syntheses and Combined Structural, Magnetic, High-Field Electron Paramagnetic Resonance, and Theoretical Studies

The trinuclear [Cu3­(RCOO)4­(H2TEA)2] copper­(II) complexes, where RCOO– = 2-furo­ate (1), 2-methoxy­benzo­ate (2), and 3-methoxy­benzo­ate (3, 4), as well as dimeric species [Cu2­(H2TEA)2­(RCOO)2]·​2H2O, have been prepared by adding tri­ethanol­amine (H3TEA) at ambient conditions to hydrated Cu­(RCOO)2 salts. The newly synthesized complexes have been characterized by elemental analyses, spectroscopic techniques (IR and UV–visible), magnetic susceptibility, single crystal X-ray structure determination and theoretical calculations, using a Difference Dedicated Configuration Interaction approach for the evaluation of magnetic coupling constants. In 1 and 2, the central copper atom lies on an inversion center, while in the polymorphs 3 and 4, the three metal centers are crystallographically independent. The zero-field splitting parameters of the trimeric compounds, D and E, were derived from high-field, high-frequency electron paramagnetic resonance spectra at temperatures ranging from 3 to 290 K and were used for the interpretation of the magnetic data. It was found that the dominant inter­action between the terminal and central Cu sites J12 is ferro­magnetic in nature in all complexes, even though differences have been found between the symmetrical or quasi-symmetrical complexes 1–3 and non-symmetrical complex 4, while the inter­action between the terminal centers, J23, is negligible.