Center metallic effect on intermolecular interactions of complexes [M(CN)5NO]x- with poly(ethylene oxide) in aqueous two-phase systems / Efeito do centro metálico nas interações intermoleculares dos complexos [M(CN)5NO]x- com o poli(óxido de etileno) em sistemas aquosos bifásicos

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

In this thesis has been studied the metallic center influences of pentacianonitrosylmetalates, [M(CN)5NO]x-, on the partition coefficient (K), of these complex anions in aqueous two-phase systems (ATPS). The ATPS were obtained by mixing stock aqueous solutions of an inorganic salt (Li2SO4 or Na2SO4) with a stock solution of poly(ethylene oxide) of average molar mass 4000 g.mol-1. The studies were carried out at four different temperatures: 278, 298, 308 and 318 K. Aliquots of 100μL of 5% (in mass) aqueous solutions of [Mn(CN)5NO]3- with different counter-ions (Na+, K+ and Mn2+) were then added to the mixture and the K values were obtained as a ratio between the complex concentration in the upper phase and that in the bottom phase. The partition behavior was evaluated with respect to the differences in concentration of components between the two phases, expressed by the parameter tie line length (TLL). It was observed that the K values increase with increasing TLL. For [Mn(CN)5NO]3-, values of K as high as 390 have been determined in the system PEO4000/Li2SO4/H2O at 278 K, while the [Cr(CN)5NO]3- concentrates in the bottom phase. The order of K values is [Cr(CN)5NO]3- <[Mn(CN)5NO]3- <[Fe(CN)5NO]2- in all ATPS and at all temperatures. The transfer process of the complexes [Mn(CN)5NO]3- and [Fe(CN)5NO]2-, based on the Haynes model, occurs with a decrease in both, enthalpy and entropy. Calorimetric measurements and non-linear vant Hoff approximation, showed that the transfer of complexes [Mn(CN)5NO]3-, from the salt rich phase to the PEO rich phase, release energy as already verified for [Fe(CN)5NO]2-. Such behavior could be attributed to specific enthalpic interactions between the complex anion and ethylene oxide (EO) segments. Infrared spectroscopy (IR) measurements indicated that stretching frequencies associated to nitrosil group, ν(NO), of Mn and Fe complexes change when these complexes are dissolved in water or in PEO, probably involving interaction of NO groups with lone pairs electrons in the oxygen atom of the EO segments. In this interacting model, the metallic center plays a key role, altering the energy levels between the orbitals 3d of the metal and 2π* orbitals of NO. This in turn changes the electronic density on the NO group through backbonding effect, which explains why the sequence of interaction [M(CN)5NO]x- PEO is [Cr(CN)5NO]3- <[Mn(CN)5NO]3- <[Fe(CN)5NO]2-.

ASSUNTO(S)

ion extraction sistemas aquosos bifásicos extração de íons aqueous two-phase systems polymero-ion interactions interações íon-polímero fisico-quimica

ACESSO AO ARTIGO

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