Abstract/Summary

Here we describe the synthesis and characterization of two new mixed-valence CoII/CoIII dimers:[(N3)CoIII(L1r)(μ-O2CR1)CoII(N3)][(N3)CoIII(L1r)(μ-O2CR1)CoII(Cl)]·2MeOH (1) and [(N3)CoIII(L2r)(μ-O2CR2)CoII(N3)][(N3)CoIII(L2r)(μ-O2CR1)CoII(OH2)]ClO4·2H2O (2) with R1CO2H = 4-nitrobenzoic acid and R2CO2H = 3-methyl-4-nitrobenzoic acid. These compounds have the same structural CoIIIO2CoIIcore topology and have been obtained with two related reduced compartmental Schiff base ligands: H2L1r = (1,3-propanediyl)bis(iminomethylene)bis(6-methoxyphenol) and H2L2r = (1,3-propanediyl)bis(iminomethylene)bis(6-ethoxyphenol), with the same N2O2O′2 donor set. The single crystal structures of both compounds display octahedral cobalt(II) centres and cobalt(III) centres with an intermediate geometry between octahedral and trigonal prism with rhombic distortion. The cobalt(III) and cobalt(II) centres are located at the inner N2O2 and outer O2O′2 compartments of the reduced Schiff base ligands, respectively. Magnetic properties show the presence of a field-induced slow relaxation of the magnetization following Direct, Raman and Orbach mechanisms.