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The crystal structural investigations of 1 : 1 (La/Nd)KFe(CN)6 4H2O (I) and 1:1 (Pr/Nd) KFe(CN)6·4H2O (II) have been determined using three-dimensional, single-crystal, X-ray diffraction data and refined by least-squares to yield final reliability (R) factors of 0.0180 and 0.020 based on 358 and 343 unique reflections, respectively. I and II crystallize in the hexagonal space group P63/m (No. 176) with a = 7.371(1), c= 13.833(3)Å for I and a = 7.362(1), c= 13.799(3) A for II. For Z = 2, the respective calculated densities are 2.371 and 2.388 mgm−3 exp., 2.369(4) and 2.382(4)mgm−3. The coordination about the lanthanide central ions in both I and II is nine, and the geometric polyhedra are tricapped trigonal prisms (TTP). Cyanide bridging links the octahedral FeC6 groups to the nine-coordinated (Ln/Nd)N6(H2O)3 groups. The noncoordinated water molecule and the potassium ion occupy holes in the lattice along the three-fold axis above and below the lanthanide ions. Selected bond distances and angles are presented as well as discussions of the synthesis, TGA, IR, and digital SEM/EDS results, and other peripheral studies of I and II.
Farmer et al. (2000) studied this question.