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Healy MR, Roebuck JW, Doidge ED, et al. Contributions of inner and outer coordination sphere bonding in determining the strength of substituted phenolic pyrazoles as copper extractants. Dalton Trans. 2016;45(7):3055-62doi: 10.1039/c5dt04055h.
Healy, M. R., Roebuck, J. W., Doidge, E. D., Emeleus, L. C., Bailey, P. J., Campbell, J., Fischmann, A. J., Love, J. B., Morrison, C. A., Sassi, T., White, D. J., & Tasker, P. A. (2016). Contributions of inner and outer coordination sphere bonding in determining the strength of substituted phenolic pyrazoles as copper extractants. Dalton transactions (Cambridge, England : 2003), 45(7), 3055-62. https://doi.org/10.1039/c5dt04055h
Healy, Mary R, et al. "Contributions of inner and outer coordination sphere bonding in determining the strength of substituted phenolic pyrazoles as copper extractants." Dalton transactions (Cambridge, England : 2003) vol. 45,7 (2016): 3055-62. doi: https://doi.org/10.1039/c5dt04055h
Healy MR, Roebuck JW, Doidge ED, Emeleus LC, Bailey PJ, Campbell J, Fischmann AJ, Love JB, Morrison CA, Sassi T, White DJ, Tasker PA. Contributions of inner and outer coordination sphere bonding in determining the strength of substituted phenolic pyrazoles as copper extractants. Dalton Trans. 2016 Feb 21;45(7):3055-62. doi: 10.1039/c5dt04055h. Epub 2016 Jan 14. PMID: 26763168.
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Dalton Trans. 2016 Feb 21;45(7):3055-62. doi: 10.1039/c5dt04055h. Epub 2016 Jan 14.

Contributions of inner and outer coordination sphere bonding in determining the strength of substituted phenolic pyrazoles as copper extractants.

Dalton transactions (Cambridge, England : 2003)

Mary R Healy, James W Roebuck, Euan D Doidge, Lucy C Emeleus, Philip J Bailey, John Campbell, Adam J Fischmann, Jason B Love, Carole A Morrison, Thomas Sassi, David J White, Peter A Tasker

Affiliations

  1. EaStCHEM School of Chemistry, University of Edinburgh, Edinburgh, EH9 EJJ, UK. [email protected] [email protected].

PMID: 26763168 DOI: 10.1039/c5dt04055h

Abstract

Alkyl-substituted phenolic pyrazoles such as 4-methyl-2-[5-(n-octyl)-1H-pyrazol-3-yl]phenol (L2H) are shown to function as Cu-extractants, having similar strength and selectivity over Fe(iii) to 5-nonylsalicylaldoxime which is a component of the commercially used ACORGA® solvent extraction reagents. Substitution in the phenol ring of the new extractants has a major effect on their strength, e.g. 2-nitro-4-methyl-6-[5-(2,4,4-trimethylpentyl)-1H-pyrazol-3-yl]phenol (L4H) which has a nitro group ortho to the phenolic hydroxyl group unit and has an extraction distribution coefficient for Cu nearly three orders of magnitude higher than its unsubstituted analogue 4-methyl-6-[5-(2,4,4-trimethylpentyl)-1H-pyrazol-3-yl]phenol (L8H). X-ray structure determinations and density functional theory (DFT) calculations confirm that inter-ligand hydrogen bonding between the pyrazole NH group and the phenolate oxygen atom stabilise the Cu-complexes, giving pseudomacrocyclic structures. Electron-accepting groups ortho to the phenol oxygen atoms buttress the inter-ligand H-bonding, enhancing extractant strength but the effectiveness of this is very dependent on steric factors. The correlation between the calculated energies of formation of copper complexes in the gas phase and the observed strength of comparably substituted reagents in solvent extraction experiments is remarkable. Analysis of the energies of formation suggests that big differences in strength of extractants arise principally from a combination of the effects of the substituents on the ease of deprotonation of the proligands and, for the ortho-substituted ligands, their propensity to buttress inter-ligand hydrogen bonding.

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