Guest-host interaction of ${\text{K}}_{0.34}\text{Co}{\left[\text{Fe}{\left(\text{CN}\right)}_6\right]}_{0.75}\cdot z{\text{H}}_2\text{O}$ as investigated by a charge-density analysis

Charge-density level structure was determined in a prototypical nanoporous material with strong guest-host interaction, ${\text{K}}_{0.34}\text{Co}{\left[\text{Fe}{\left(\text{CN}\right)}_6\right]}_{0.75}\cdot z{\text{H}}_2\text{O}$($z=3.6$ and 2.7). We determined atomic coordinates and occupancies $\left(g\right)$ of three kinds of oxygen sites of guest waters, i.e., zeolite water, ligand water, and off-axis water, as a function of $z$. The variation in $g$ against $z$ indicates easily removable nature of the zeolite and off-axis waters, and robust coordination bond with the ligand water. Significant change in the charge density of the host-NC-Fe-CN-Co-NC-Fe-CN-lattice revealed hybridization effect between the off-axis water and the adjacent Co atom.

Figure 1

(Color online) (a) Isosurface of MEM charge density at $0.6e/{\text{Å}}^3$ of ${\text{K}}_{0.34}\text{Co}{\left[\text{Fe}{\left(\text{CN}\right)}_6\right]}_{0.75}\cdot 3.6{\text{H}}_2\text{O}$ around the Co-NC-Fe bond and K atom. The charge density was estimated based on a series of structure factors $F_{hkl}$ determined based on the structural mode without oxygen. Spheres represent extra charge density due to oxygen. (b) Isosurface at $0.6e/{\text{Å}}^3$ of ${\text{K}}_{0.34}\text{Co}{\left[\text{Fe}{\left(\text{CN}\right)}_6\right]}_{0.75}\cdot 3.6{\text{H}}_2\text{O}$ around the Co-NC-Fe bond and K atom. The charge density was estimated based on the $F_{hkl}$ series determined based on the structural model with the oxygen.

Figure 2

(Color online) (a) MEM charge density of ${\text{K}}_{0.34}\text{Co}{\left[\text{Fe}{\left(\text{CN}\right)}_6\right]}_{0.75}\cdot 3.6{\text{H}}_2\text{O}$ $\left(z=3.6\right)$ for the (100) section containing Fe, Co, C, and N atoms at 90 K. (b) Charge density of ${\text{K}}_{0.34}\text{Co}{\left[\text{Fe}{\left(\text{CN}\right)}_6\right]}_{0.75}\cdot 2.7{\text{H}}_2\text{O}$ $\left(z=2.7\right)$ for the (100) section at 90 K. Contour lines are drawn from 0.35 to $3.0e{\text{Å}}^{-3}$ at intervals of $0.5e{\text{Å}}^{-3}$.