Synthesis of Cyano-Bridged Magnetic Nanoparticles Using Room-Temperature Ionic Liquids

A principally new exploit of ionic liquids as an alternative reaction medium in the synthesis of cyano‐bridged coordination‐polymer nanoparticles is reported. Stable colloid solutions containing nanoparticles of cyano‐bridged molecule‐based magnets, M3[Fe(CN)6]2/[RMIM][BF4] (M2+=Ni, Cu, Co) and Fe4[Fe(CN)6]3/[RMIM][BF4] (R=1‐butyl (BMIM), 1‐decyl (DMIM)), were prepared in the corresponding 1‐R‐3‐methylimidazolium tetrafluoroborate [RMIM][BF4], which acts as both a stabilising agent and a solvent. By varying the length of the N‐alkyl chain on the imidazolium cation of [RMIM]+ and the temperature, the growing process can be controlled to produce nanoparticles of different sizes. By studying the magnetic properties of frozen colloids it is shown that the relaxation of magnetisation is strongly influenced by interparticle interactions, which leads to the appearance of spin‐glass‐like dynamics in these systems. One liquid, two roles: Room‐temperature ionic liquids (RTILs) have been used for the synthesis of nonaggregated, uniformly sized, spherical, cyano‐bridged magnetic nanoparticles (see figure). The RTILs act as both the stabilising agent and solvent, so no additional ligand is required to obtain stable colloidal solutions.