Precise Electrochemical Control of Ferromagnetism in a Cyanide-Bridged Bimetallic Coordination Polymer

Magnetic coordination polymers can exhibit controllable magnetism by introducing responsiveness to external stimuli. This report describes the precise control of magnetism of a cyanide-bridged bimetallic coordination polymer (Prussian blue analogue: PBA) through use of an electrochemical quantitative Li ion titration technique, i.e., the galvanostatic intermittent titration technique (GITT). K0.2Ni[Fe(CN)(6)](0.7)center dot 4.7H(2)O (NiFe-PBA) shows Li ion insertion/extraction reversibly accompanied with reversible Fe3+/Fe2+ reduction/oxidation. When Li ion is inserted quantitatively into NiFe-PBA, the ferromagnetic transition temperature T-C gradually decreases due to reduction of paramagnetic Fe3+ to diamagnetic Fe2+, and the ferromagnetic transition is completely suppressed for Li-0.6(NiFe-PBA). On the other hand, T-C increases continuously as Li ion is extracted due to oxidation of diamagnetic Fe2+ to paramagnetic Fe3+, and the ferromagnetic transition is nearly recovered for Li-0(NiFe-PBA). Furthermore, the plots of T-C as a function of the amount of inserted/extracted Li ion x are well consistent with the theoretical values calculated by the molecular-field approximation.