Neutron Diffraction and EXAFS Studies of K2x/3Cu[Fe(CN)6]2/3•nH2O

The crystal structure of copper hexacyanoferrate (CuHCF), K2x/3Cu[Fe-(CN)(6)](2/3)center dot nH(2)O, with nominal compositions x = 0.0 and x = 1.0 was studied by neutron powder diffraction (NPD) and extended X-ray absorption fine structure (EXAFS) spectroscopy. The compound crystallizes in space group Fm (3) over barm, with a = 10.1036(11) angstrom and a = 10.0588(5) angstrom for x = 0.0 and x = 1.0, respectively. Difference Fourier maps for x = 0.0 show that the coordinated water molecules are positioned at a site 1921 close to vacant N positions in the -Fe-C-N-Cu- framework, while additional zeolitic water molecules are distributed over three sites (8c, 32f, and 48g) in the -Fe-C-N-Cu- framework cavities. The refined water content for x = 0.0 is 16.8(8) per unit cell, in agreement with the ideal 16 (n = 4). For x = 1.0, the refinement suggests that 2.6 K atoms per unit cell (x = 0.98) are distributed only over the sites 8c and 32f in the cavities, and 13.9(7) water per unit cell are distributed over all the four positions. The EXAFS data for Fe, Cu, and K K-edges are in agreement with the NPD data, supporting a structure model with a linear -Fe-C-N-Cu- framework and K+ ions in the cavities.