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.
It is demonstrated here that it is possible to determine mercury in chloride containing media like seawater by anodic stripping voltammetry using a modified electrode. A gold microwire electrode is modified using mercaptoacetic acid (MAA) to eliminate the problem of calomel formation, allowing the mercury to become fully removed from the electrode surface after each scan. In a synthetic salt solution of KNO 3 the sensitivity for mercury was found to be improved by the surface modification. In seawater the sensitivity was not significantly improved possibly because of complexation of the mercury by the abundant chloride; however, the MAA coating prevented the formation of calomel causing the background scan to be free of mercury. Measurements in seawater at various pH values demonstrated that mercury detection is possible at natural pH (around 8); however, best sensitivity was attained at pH 4.8 with a deposition time of 3 min. A peak for copper occurred at more negative potential but did not interfere at this pH. The calibration was linear between 0 and 37 nM mercury with a limit of detection of 1 nM mercury.
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.,
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