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PEO−[M(CN) 5 NO] x - (M = Fe, Mn, or Cr) Interaction as a Driving Force in the Partitioning of the Pentacyanonitrosylmetallate Anion in ATPS: Strong Effect of the Central Atom

2008; American Chemical Society; Volume: 112; Issue: 37 Linguagem: Inglês

10.1021/jp711617z

ISSN

1520-6106

Autores

Luís Henrique Mendes da Silva, Maria do Carmo Hespanhol da Silva, Kelly R. Francisco, Marcus V. C. Cardoso, Luís Antônio Minim, Jane Sélia dos Reis Coimbra,

Tópico(s)

Polyoxometalates: Synthesis and Applications

Resumo

The partitioning behavior of pentacyanonitrosilmetallate complexes—[Fe(CN)5NO]2−, [Mn(CN)5NO]3−, and [Cr(CN)5NO]3−—has been studied in aqueous two-phase systems (ATPS) formed by adding poly(ethylene oxide) (PEO; 4000 g mol−1) to an aqueous salt solution (Li2SO4, Na2SO4, CuSO4, or ZnSO4). The complexes partition coefficients (Kcomplex) in each of these ATPS have been determined as a function of increasing tie-line length (TLL) and temperature. Unlike the partition behavior of most ions, [Fe(CN)5NO]2− and [Mn(CN)5NO]3− anions are concentrated in the polymer-rich phase with K values depending on the nature of the central atom as follows: K [Fe (CN) 5 NO] 2− ≫ K [Mn (CN) 5 NO] 3− > K [Cr (CN) 5 NO] 3− . The effect of ATPS salts in the complex partitioning behavior has also been verified following the order Li2SO4 > Na2SO4 > ZnSO4. Thermodynamic analysis revealed that the presence of anions in the polymer-rich phase is caused by an EO−[M(CN)5NO]x− (M = Fe, Mn, or Cr) enthalpic interaction. However, when this enthalpic interaction is weak, as in the case of the [Cr(CN)5NO]3− anion ( K [Cr (CN) 5 NO] 3− < 1), entropic driving forces dominate the transfer process, then causing the anions to concentrate in the salt-rich phase.

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