Salicylaldehyde hydrazones: buttressing of outer sphere hydrogen-bonding and copper-extraction properties

Roach, B. D., Lin, T., Bauer, H., Forgan, R. S. , Parsons, S., Rogers, D. M., White, F. J. and Tasker, P. A. (2017) Salicylaldehyde hydrazones: buttressing of outer sphere hydrogen-bonding and copper-extraction properties. Australian Journal of Chemistry, 70(5), pp. 556-565. (doi:10.1071/CH16639)

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Abstract

Salicylaldehyde hydrazones are weaker copper extractants than their oxime derivatives, which are used in hydrometallurgical processes to recover ~20 % of the world’s copper. Their strength, based on the extraction equilibrium constant Ke, can be increased by nearly three orders of magnitude by incorporating electron-withdrawing or hydrogen-bond acceptor groups (X) ortho to the phenolic OH group of the salicylaldehyde unit. Density functional theory calculations suggest that the effects of the 3-X substituents arise from a combination of their influence on the acidity of the phenol in the pH-dependent equilibrium, Cu2+ + 2Lorg ⇌ [Cu(L–H)2]org + 2H+, and on their ability to ‘buttress’ interligand hydrogen bonding by interacting with the hydrazone N–H donor group. X-ray crystal structure determination and computed structures indicate that in both the solid state and the gas phase, coordinated hydrazone groups are less planar than coordinated oximes and this has an adverse effect on intramolecular hydrogen-bond formation to the neighbouring phenolate oxygen atoms.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Forgan, Dr Ross
Authors: Roach, B. D., Lin, T., Bauer, H., Forgan, R. S., Parsons, S., Rogers, D. M., White, F. J., and Tasker, P. A.
College/School:College of Science and Engineering > School of Chemistry
Journal Name:Australian Journal of Chemistry
Publisher:CSIRO Publishing
ISSN:0004-9425
ISSN (Online):1445-0038
Published Online:01 February 2017
Copyright Holders:Copyright © 2017 The Authors
First Published:First published in Australian Journal of Chemistry 70(5):556-565
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
619471Biomimetic guest selective metal-organic frameworks: catalysis and self-assemblyRoss ForganEngineering & Physical Sciences Research Council (EPSRC)EP/L004461/1CHEM - CHEMISTRY