Magnetic Properties of Dimeric Copper(II) Trichloroacetate Adducts with 3-Substituted Pyridines

Dimeric copper(II) trichloroacetate adducts with 3-substituted pyridines, [Cu(Cl3CCOO)2(3-Xpy)]2 where X=Cl, Br, H, CN, and CH3, have been prepared. Magnetic susceptibility and ESR data show that both the singlet–triplet separation (−2J) and the zero field splitting (D) decrease in the order: 3-Clpy adduct (193 and 0.397 cm−1)≈3-Brpy adduct (191 and 0.399 cm−1)>py adduct (188 and 0.385 cm−1)>3-CNpy adduct (138 and 0.216 cm−1)>3-CH3py adduct (83 and 0.182 cm−1). Electronic spectra indicate that the adducts with X=Cl, Br, and H have a distorted square-pyramidal copper(II) geometry and that those X=CN and CH3 have a distorted trigonalbipyramidal geometry. Form these results, it is concluded that the strength of antiferromagnetic interaction in [Cu(Cl3CCOO)2(3-Xpy)]2 complexes decreases as the distortion of copper(II) geometry increases from squarepyramid toward trigonal-bipyramid.