Substitutional solid solutions of metal hexacyanometalates in which low-spin iron(III) and cobalt(III) ions populate the carbon-coordinated sites were synthesized and studied by powder diffraction including Rietveld refinement, cyclic voltammetry of immobilized microparticles, diffuse reflection vis-spectrometry, and magnetization techniques. The continuous solid solution series of potassium copper(II), potassium nickel(II), and iron(III) [(hexacyanoferrate(III))(1-x)(hexacyanocobaltate(III))(x)] show that the substitution of low-spin iron(III) by cobalt(III) in the hexacyanometalate units more strongly affects the formal potentials of the nitrogen-coordinated copper(II) and high-spin iron(III) ions than those of the remaining low-spin iron(III) ions. In the case of copper(II) and iron(III) [(hexacyanoferrate(III))(1-x)(hexacyanocobaltate(III))(x)] the peak currents decrease much more than can be explained by stoichiometry, indicating that the charge propagation is slowed by the substitution of low-spin iron(III) by cobalt(III). The Rietveld refinement of all compounds confirmed the structure initially proposed by Keggin for Prussian blue and contradicts the structure described later by Ludi. The dependencies of lattice parameters on composition exhibit in all series of solid solutions studied similar, although small, deviations from ideality, which correlate with the electrochemical behavior. Finally, a series of solid solutions of the composition KNi(0.5)(II)Cu(0.5)(II)[Fe(III)(CN)(6)](1-x)[Co(III)(CN)(6)](x), where both the nitrogen- and carbon-coordinated metal ions are mixed populated and were synthesized and characterized. These are the first examples of solid solutions of metal hexacyanometalates with four different metal ions, where both the nitrogen- and the carbon-coordinated sites possess a mixed population.

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The series of spinels was prepared by ceramic technology. The crystal structures were refined from the x-ray diffraction data using the Rietveld profile method. The high-temperature magnetic susceptibility was measured by the Faraday method in the temperature range 290 - 600 K and the data were fitted to the Curie - Weiss law. The cation distribution in these diluted magnetics is obtained from x-ray diffraction and high-temperature magnetic susceptibility measurements. It was found that, for , ions occupy exclusively the octahedral position in the spinel type of structure. In the low-concentration region a strong clustering of magnetic ions is observed. In the range , ions are distributed in both tetrahedral and octahedral cationic sites. The Curie - Weiss paramagnetic temperature is negative in the whole range of concentrations, as the consequence of a predominant antiferromagnetic interaction. The appearance of the ions in tetrahedral sites (around x = 1.33) leads to a drop in the absolute -value. The effective magnetic moments of ions are about for and depend on the concentration for x>1.33.

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are synthesized by precipitation from solutions of K 3 [M(CN) 6 ] (M: Co, Fe), CuCl 2 , Ni(NO) 2 , and Fe(NO 3 ) 3 . The samples are characterized by powder XRD, cyclic voltammetry, diffuse reflection VIS spectroscopy, and magnetization techniques. These compounds form a continuous series of mixed crystals, where the substitution of low-spin Fe(III) by Co(III) shows thermodynamic effects on the formed potentials and kinetic effects on the voltammetric peak currents. All compounds have the structure (space group Fm3m) proposed by Keggin for Prussian blue. -(WIDMANN, A.; KAHLERT*, H.; PETROVIC-PRELEVIC, I.; WULFF, H.; YAKHMI, J. V.; BAGKAR, N.; SCHOLZ, F.; Inorg. Chem. 41 (2002) 22, 5706-5715; Inst. Chem. Biochem., Ernst-Moritz-Arndt-Univ.,