New symmetrical binucleating ligands N,N-bis[2-hydroxy-5-methyl-3-(4-methyl-piperazinomethyl)benzyl]-alkylamines L1 and L2 and their copper(II) complexes [Cu2L(X)2]·2H2O, where X = CH3COO−, C6H5COO−, Cl−, and ClO4-, were prepared and characterised. All the complexes undergo quasi-reversible reduction at negative potential (E = −0.48 to −1.02 V). The acetate and benzoate complexes undergo a two-step single electron transfer at –0.48 to –0.60 V and −0.9 to −1.02 V. The chloro and perchlorate complexes undergo a single step two-electron transfer at −0.55 to −0.75 V. Variable temperature magnetic studies show the presence of weak exchange interaction for acetate (−2 J around 25 to 40 cm−1) and benzoate (−2 J around 45 to 55 cm−1) bridged complexes and no exchange interaction is found for chloro and perchlorate complexes. ESR spectra of chloro and perchlorate complexes are like mononuclear copper(II) complexes with hyperfine splitting (A = 165 ± 5, g∥ = 2.17–2.23, and g⊥ = 2.05–2.10). The ESR spectra of acetate and benzoate complexes are like binuclear copper(II) complexes with broad signal (g = 2.2).
Weak exchange striction between the
4f
and
3d
ions in the multiferroic
GdMn2O5