Magnetic Study of a Pentanuclear {Co2IIICo3II} Cluster with a Bent {CoII3} Motif

We have synthesised and structurally characterised a new pentanuclear mixed-valent cobalt cluster of formula [(Co3Co2III)-Co-II(OH)(2)(piv)(6)(L)(2)(H2O)(4)] (piv = trimethylacetate, H2L = salicylideneanthranillic acid) from reaction of a dinuclear cobalt pivalate precursor with a Schiff base type ligand under mild reaction conditions. The core structure can be conveniently described as two fused Co-3-(3)-OH triangles with a strict unique sharing vertex point. A complete picture of the magnetic behaviour of this compound is presented. Through combined use of susceptibility, magnetisation, and EPR data as well as broken-symmetry DFT calculations, we have supported the magnetic data that show weak and anisotropic exchange interaction between Co-II ions affording an S-eff = 1/2 ground state that is not completely isolated from the low-lying excited doublets at low temperature. Under the optimum applied field of 2 kOe, a frequency-dependent out-of-phase susceptibility signal can be observed below 4 K. However, no reliable relaxation rates could be extracted due to the narrow temperature range in which this behaviour was observed.