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

Abstract

The crystal structure of copper hexacyanoferrate (CuHCF), K2x/3Cu[Fe(CN)6]2/3·nH2O, 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 Fm3m, with a = 10.1036(11) A and a = 10.0588(5) A 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 192l 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...