Metal(II) Hexacyanochromate(III) MCr (M = Co, Cu, Fe) Coordination Nanoparticles Stabilized by Alkyl Surface Coordination Ligand: Downsizing Effect on Their Crystal Structure and Magnetic Properties

We have reported the reversed micelle synthesis and isolation of metal(II) hexacyanochromate(III) MCr (M = Co, Cu, Fe) coordination nanoparticles, which are protected by alkyl surface coordination ligand of 4-(dioctadecylamino)pyridine (OPy). The dependence of their physicochemical (shape, size, crystal structure, and electronic state) and magnetic properties on the metal constituent and the downsizing effect was investigated by comparing the MCr (M = Co, Cu, Fe) nanoparticles with their bulk crystals. These compounds were precisely characterized by transmission electron microscopy observation, UV−vis, elementary analysis, Fourier transform infrared, X-ray diffraction, and direct current and alternating current (ac) magnetic studies. The shape and diameter of MCr (M = Co, Cu, Fe) nanoparticles, which differ in metal constituents, are cubic particles of 9.06 ± 0.68 (M = Co), subround particles of 15.71 ± 1.81 (M = Cu), and cubic particles of 10.01 ± 0.84 (M = Fe) nm. The MCr (M = Co, Fe) nanoparticles show typical face-centered cubic structure as their bulk crystals; however, the CuCr nanoparticle shows unexpected crystal structure, different from the CuCr bulk crystal. In the case of FeCr compounds, linkage isomerism is observed not only in bulk crystal but also in nanoparticles. Additionally, the magnetic properties of FeCr nanoparticles are influenced by the additive amount of OPy. The MCr (M = Co, Cu, Fe) nanoparticles show strong frequency dependence in both real and imaginary components of the ac magnetic susceptibility.