Kinetic and mechanistic aspects of copper(II) coordination to bis-N,N ′-(salicylidene)-1,2-diaminoethane-based hydrogel polymer membranes, and the permeation of cations through them

Abstract

A range of hydrophilic membranes composed of copolymers of bis-N,N′-(5-vinylsalicylidene)-1,2-diaminoethane with 2-hydroxyethylmethacrylate have been synthesised. Over a period of approximately 2 h these membranes coordinate copper(ii) ions from aqueous solution to yield tetradentate species in a first-order process. However, only a small fraction of the potentially ligating sites are fully used in this way. Kinetic studies of the interactions with the nitrate, chloride and sulfate salts of copper(ii) are described and a detailed mechanism is proposed. Molecular rotations at the ligand site are suggested to be the rate determining steps of the overall process. Values of individual rate and equilibrium constants have been determined, and shown to be consistent with the equivalent data found for simpler ligands involved in reactions in homogeneous solutions. The permeation of the nitrates of Co^II , Ni^II and Cu^II through membranes of these copolymers is also described. Due to the slow rates of complex formation, the ligand sites have no significant effect on either the permeability of the salts through the membrane, or the time lags before salt passage is detected. For comparison purposes, permeation data for the passage of the nitrate of the substitutionally inert [Cr(H₂O)₆ ]³⁺ ion through 4-methyl-4′-vinyl-2,2′-bipyridyl-containing membranes are also reported.

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