The ferrocyanide structures of transition metals (M) Ti2+, Cr2+, Mn2+, or Co2+ are investigated using a first-principles modeling approach. The crystal structure of cobalt ferrocyanide is found to resemble previous experimental data with good accuracy (∼1% error). The considered porous structures possess magnetic moments of 8.00 μ B/cell, 8.00 μ B/cell, 4.00 μ B/cell, and 4.00 μ B/cell given by the [TiFe(CN)6]2-, [CrFe(CN)6]2-, [MnFe(CN)6]2-, and [CoFe(CN)6]2- frameworks, respectively. There is only one spin-state occupation at the Fermi level, which leads to the conclusion of semi-metallicity of the four structures. To verify the reliability of the electronic and magnetic properties, linear-response DFT + U calculations are performed and establish excellent agreement with the conventional DFT calculations. Then, the mechanical strength is evaluated by estimating the bulk moduli of the four structures, which fall in the range of 114 GPa-133 GPa. Upon the consideration of one C ≡ N- linker defect, the magnetic moments of cobalt ferrocyanide and manganese ferrocyanide rise dramatically to 8 μ B/cell, while that of the titanium structure drops to 6 μ B/cell. In light of the electronic structure evidence, we believe that the low-spin Fe cation nearby the C ≡ N- defect has an indirect effect on spin polarization of the four Co cations in the unit cell.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Acoustics and Ultrasonics
- Surfaces, Coatings and Films