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Selectivities and Thermodynamic Parameters of Alkali-metal and Alkaline-earth-metal Complexes of Polyethylene Glycol Dimethyl Ethers in Methanol and Acetonitrile by Ng. van Truong; A.R. Norris; H.S. Shin; E. Buncel; R.A.B. Bannard; J.G. Purdon is a Chemistry article available to read on EtoBox.

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Thermodynamic parameters (log K,, AH=, TAS,) of alkali-metal and alkaline-earth-metal ion complexes of polyethylene glycol dimethyl ethers (glymes) have been determined in methanol and acetonitrile as solvents at 2.5 "C by using a modified calorimetric technique. It has been shown that, for a given number of donor sites, the stabilities of M+ and M2+ complexes by glymes are lower than those of the corresponding macrocyclic polyethers and open chain antibiotic anions of the Nigericin group by a factor of up to 10'. The stability constants (log&) of the cation-glyme complexes are higher in acetonitrile than in methanol. The selectivities towards alkali and alkaline-earth cations with similar ionic radii (e.g. K&Ca\*+)/K,(Na') and K,(Ba\*+)/K,(K+)) of the glymes are also low. This may result from less effective shielding of the cation from cation-solvent interactions in the glymes as compared to crown ethers and open-chain antibiotic anions. In both solvents, the stability constant of a given metal complex increases monotonically with increase of the glyme chain length. The stability of K+ and Ba2+ complexes by glymes is largely enthalpy dominated, accompanied by an unfavourable entro

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Author

Ng. van Truong; A.R. Norris; H.S. Shin; E. Buncel; R.A.B. Bannard; J.G. Purdon

Publisher

Elsevier Science; Elsevier ; Elsevier BV (ISSN 0020-1693)

Published

1991

Language

EN

Field

Chemistry (Physical Sciences)