Properties of [Fe4Cu2] magnetic cluster compound

We have designed and synthesized a novel magnetic cluster containing low-spin (S = 1/2) Fe3+ and spin-1/2 Cu2+ ions, which incorporates competing ferromagnetic Fe–Cu interactions and antiferromagnetic Fe–Fe and Cu–Cu interactions. This is achieved with the help of a cyanido-bridged hexanuclear iron-copper cluster [{Fe(Tp)(CN)3}4{Cu(MePz)2}2] following the building block approach. All experiments were carried out using the stable compound, [{Fe(Tp)(CN)3}4{Cu(MePz)2}2], after removing the solvent molecules at 110°C for 2 h. Unusual magnetic interactions in this compound are revealed by the temperature- and field-dependent dc magnetic measurements. These magnetic measurements indicate the existence of ferromagnetic interactions between the low-spin Fe3+ and Cu2+ ions via cyanide bridge dominating magnetic properties over a wide temperature range below ~15 K. At a still lower temperature, magnetic properties appear to be controlled by an effective antiferromagnetic interaction, possibly arising from inter-cluster couplings. Frequency-dependent ac susceptibility measurements establish a possible glassy state emerging below 4 K.